Servo - July 2011

GEERHEAD

Distinct from this approach is a screw shaped microbot with embedded magnetic material that physicians could some day drive through tissue wirelessly. This approach can enable moving through soft tissue and not just inside veins. This approach requires the helix to make only one full rotation to move the length of the microbot through human tissue. The other helix-propelled bots must turn the helix several times to move through human fluid.

Another propulsion method for microbots is the traveling wave. Traveling wave propulsion looks like a fish tail swimming behind the microbot. Traveling waves are more efficient at propulsion than propellers, assuming the efficiency of the actuation is equal to that of the propeller system. However, there are fabrication, power, and control issues related to creating distributed actuation for the traveling wave method. Methods that create traveling waves without distributed actuation are more feasible but less efficient.

Modular, Self-Assembling Mini Medical Robots

In another approach to microbots, researchers are adding active locomotion and telemetry to capsule endoscopy technology. According to IRIS, the size of the capsule cannot be larger than what a person can swallow. In this new method, the larger robot would be swallowed in individual pieces that would assemble themselves inside the gastrointestinal tract. Self-assembly is the biggest challenge to this approach.

By using magnets on the faces of the modules that

Resources

Institute of Robotics and Intelligent Systems www.iris.ethz.ch

Research of Professor Bradley J. Nelson www.iris.ethz.ch/msrl/research

12 SERVO 07.2011

This is an image of the Octomag. In the background, you can see an image as viewed through an ophthalmic microscope.

must connect to one another, researchers hope to solve the self-assembly problem. The results are promising for a snaking robot that can assemble itself and make its way through the small intestine.

The self-assembling robot would have sensors on its front end to detect pathologies that would wirelessly communicate to the surgeon or physician. A module designed for specific tasks would execute commands to accomplish the task once an actuation module moves the robot into the right place. Sensors and actuators that work on individual pill sized devices are already being developed. Each sensor or actuator could eventually constitute a module in the larger robot discussed here.

Eye See the Robot

One application of microbots is retinal therapies where the robot could help the surgeon operate inside the human eye. The primary challenge to this approach is localization. Because researchers and clinicians can easily see what is in the eye, they can look through the eyeball to localize the robot. Using high quality imaging of the rear of the human eye, they can develop algorithms to track and localize the microbots. However, there is no existing research that explains what the effects of this will be.

IRIS researchers have developed a mechatronic vitreoretinal ophthalmoscope that can take an image of the entire retina despite the obstruction of view created by the other parts of the eye. They can use this device to image and follow objects in the retina. There is on-going research to discover how much illumination will be necessary to follow objects in the human eye.

The imaging device must be able to differentiate the microbot from the rest of the retina. The mechatronic device must use several lenses to see beyond the other components of the eye to keep the retina in view. Images are still blurry much of the time. The light that reaches the eye’s interior can decrease the quality of the images taken due to uneven brightness. The microbot has no distinctive colors to distinguish it from the rest of the eye.

IRIS researchers have surmounted many of these obstacles by using trained color histograms, colorspace evaluation, and maximum separability thresholding. According to IRIS, a real time color tracker in the right color space assures that the microbot can be separated from the rest of the eye.