The large development of computer assisted surgery has encouraged the miniaturisation of intracorporeal robots. For that, continuum and cannula robots are studied worldwide and their design, modeling, fabrication, and control constitute hot topics. Our team propose the study of embedded actuator based concentric tube robots in order to improve the performances of this interesting robot kinematic. We are focusing on Electro-Active Polymer (EAP) for the actuation of cannula robots and their combination with efficient available actuators (SMA, tendon-driven, etc.).

Design & Modeling

The objective is to develop innovative designs and the use of smart actuators combined with cutting edge mechanisms in order to overcome the limitations of actual designs. The approach to model the continuum structure is also figured out by keeping in head the final objectives: the optimization of the proposed design and the model-based control. Basically the trade off has to be made between the accuracy then the complexity of the model, which enables to well describe the robot behaviour, and the computation time. The final choice depends on the task requirements.

Different hypothesis are developed: piecewise constant curvature (PCC), Euler–Bernoulli beam theory, Cosserat rod with Kirchhoff hypothesis, etc.

Continuation method and bifurcations analysis are used in order to understand complex behaviour of soft continuum robots (stability, multiple solutions to forward kinematics, non linearities, etc.). The proposed computational analysis was applied to concentric tube robots and magnetic continuum robots. It is done in collaboration with ICube - AVR Strasbourg.

Fabrication & Control

The challenge is to fabricate the proposed design with the considered scale by using conventional machining, 3D printing and micromachining. It is quite cumbersome to miniaturize mechanisms/actuators then the technological development is one core of this task.

Afterward, the control of the continuum robots is achieved by using the models previously established and appropriate sensors (magnetic tracker, camera, etc.). The challenge is to get accurate, fast, and repeatable behavior of the robot.

We are investigating the sensor-based control of soft continuum robots. Various sensors (camera, electromagnetic tracker, OCT, US, MRI, etc.) could be used according to the application constraints. For example, we have recently demonstrated the achievement of 10 µm positioning accuracy (in 2D) of CTR by using OCT feedback.