Simulation is more than Software

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Optimization of the Dexter® surgical robot
Dexter is a robotic surgery system designed by Distalmotion that gives surgeons direct access to both the patient and the robot. This concept is called on-demand robotics.

Simulation of the gravity compensation mechanism on the DEXTER surgical robot with Ansys Workbench

Sector: Health, Medical technologySpecialist field: Structural mechanics

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.

Summary

Task

The surgeon console is a key component of the Dexter system. It is responsible for precisely capturing the surgeon’s hands movements in order to transmit them to the robotic arms that operate the surgical instruments. The project aims to identify the failure mode of the transmission system during the development of a working prototype and to optimize its design.

Solution

Simulation allowed for a significant simplification of the final design by removing the intermediate arm, thus reducing the total deformation by 50% and achieving homogeneous behavior, regardless of the position.

Customer benefits

Distalmotion benefits at two levels from its relationship with CADFEM, which provides support through the Ansys Startup Program and in the implementation of simulations, thus enabling its products to be made reliable very quickly.

Project Details

Task

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.

During the development of a working prototype, it was observed that the balancing mechanism worked perfectly for the first degree of freedom but was not optimal for the second degree of freedom, showing a noticeable variable displacement force in certain areas of the workspace. It was quickly identified that the problem came from the force transmission system between the first and second degrees of freedom, a parallelogram mechanism. The goal of this project is to identify the failure mode of the transmission system and to optimize its design in order to achieve the objectives in terms of user-friendly and precise handling.


Customer Benefit

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.


Solution

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.


Head of Engineering

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