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Robot assisted operations with tactile dexterity

Robot assisted operations with tactile dexterity If miniaturised endoscopy robots lack one thing, then it is haptic feedback for the surgeon, who wants not only to see but also feel what he is doing. To this end, masters student Florian Klug at Darmstadt Technical University has developed a force-feedback user interface.

The interface is that boundary where the surgeon's hand contacts the robot which carries out the surgical procedures during an invasive operation. It is a manually-operated control device, in principle similar to a joystick. It can grasp, cut and sew - everything a surgeon would do with conventional instruments - with its miniature instruments moved by means of three push rods that are connected to the user interface.

The interface is controlled by the thumb, index and middle fingers. Importantly, when the index finger moves a lever, force is applied in the opposite direction so that the surgeon effectively feels a real-world resistance.

When the surgeon grips, an encoder in the user interface registers the position and movement of the fingers. The position information is passed on to the robot, which moves its gripper accordingly. At the same time, the pressure that is being applied between the tissue and jaws is measured at the jaws. This force is further conveyed by a motor in the user interface to the surgeon's fingers. The transmission of force is provided by brushless DC-motors from Faulhaber, available in the UK from EMS, which offer high torque and minimum weight.

Whenever a pinching action is made, the surgeon's movements are transmitted by a cable-pulley linkage. Here, a static gripping force of up to 6.3N is translated and output opposite the direction of gripping. A brushless direct current motor also serves as a source of torque for rotational motion. A coupled toothed-belt drive delivers the desired gearing.

Klug says: "My aim was to convey an adequate sense of touch to the surgeon for actuating the robotic hand. He should have the feeling that he is essentially operating with his own fingers. Previous interfaces have only partially succeeded in doing this."

Commenting on his choice of Faulhaber motors, Klug says: "Because an operation can take several hours, the weight of the user interface is critical. The entire interface only weighs 257 grams - to no small extent thanks to the Faulhaber motors. Relative to their weight, they deliver the greatest torque.

"Moreover, the motors and encoders have a very high resolution and work with extreme precision," he continues. "Also, last but not least, the AES encoder requires an absolute minimum of wiring. Because all of the wires must be accommodated in a finely-detailed structure, that is a significant benefit."
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