Micro-robots and airplanes with FEA
A self-propelled, remote-controlled micro-robot revolutionizes heart surgery via more effective "peep hole operations" - and the same technology also leads to cheaper flights by reducing the air resistance around an aircraft in half.
Introduction
The actual prototype.
These widely differing applications may be the result of a basic research project on micro-robots at the Royal Institute of Technology in Stockholm. On May 26, 2000, the researcher, Thorbjörn Ebefors, defended his doctoral dissertation, "Polyimide V-groove Joints for Three-Dimensional Silicon Transducers" at the Department of Signals, Sensors and Systems. The secret and the common denominator behind these wide-ranging applications is a small plastic hinge initially designed for mobile sensors in measuring equipment for aerodynamic flows. In the course of the project, it turned out that the same hinge could also be used to build a walking robot in micro format. Large medical technical companies and Boeing in the aircraft industry have already indicated great interest in the project, even though the practical applications still lie at least ten years in the future.
Micro eddy-current brakes
When the project began, Thorbjörn and his research colleagues at the Royal Institute of Technology and Chalmers University of Technology realized that the resistance to an object's motion in flowing air depends on small eddy currents formed at the object's rear. This meant that if these eddy currents could be measured and affected arbitrarily, air resistance (and thereby energy costs) could be reduced considerably, irrespective of the shape of the body. The prerequisite to this result, however, is that these eddy currents must be measured with great accuracy, which the 2D sensors currently found on the market are not able to provide. Of course in the laboratory environment, 3D sensors are found but none of the traditional constructions are sufficiently accurate. But with Thorbjörn's mobile, hair-like silicon sensors, it is possible.
Thorbjörn Ebefors, researcher at the Department of Signals, Sensors and Systems at the Royal Institute of Technology in Stockholm.
The sensors must be able to be moved easily without wearing out too quickly. By means of extensive FEM calculations, the researchers concluded that 3 - 7 small V-shaped fillings of an extremely temperature-sensitive and durable plastic polyimide should be inserted in a "fly leg". It can then easily be deflected to move concurrently with the micro eddy currents formed around the object on which they are mounted.
Micro-robot spin-off project
At the end of 1996, Thorbjörn and his colleagues decided to use the same hinge to develop a walking micro-robot that looks like a small microchip with moving legs. The construction consists of a small silicon chip and legs also made of silicon. With the same V-shaped hinge, the legs are bent when a voltage is applied. The prototype found today is 5 mm wide and 15 mm long and moves 1 mm/second, carrying 50 times its own weight. Currently, energy is supplied externally with thin gold wires since a button cell battery does not provide sufficient voltage. With more effective batteries in the future, however, robots will be able to carry their own power source. They will also be equipped with a prehensile claw, remote controlled by radio signals. The robot should accordingly be able to "promenade" into a vein in the body and clean up calcifications and anything else. They will also be considerably smaller than the prototype found at the Royal Institute of Technology.
Growth Areas
- Microelectronics and micro-mechanics are two extremely important growth areas for today's industrial society, says Thorbjörn Ebefors. And it is not only doctors who need robots. They are also needed for assembling complex systems in which very small micro- electrical (IC), micro-optical and micro-mechanical components will be assembled into functioning systems.
From a production standpoint, the new robots must be developed by printing and etching the plastic in a silicon slice in two dimensions. Just as large numbers of transistors are concentrated on a silicon chip today, in the future it will be possible to mass-produce robots and thereby reduce the unit cost.
A prerequisite for being able to develop new technology quickly is multiple "what-if" analyses in which the properties of a prototype can be modeled precisely without building a new one each time. To this end, COMSOL Multiphysics has proven to be very useful. Another big advantage is also that COMSOL Multiphysics runs in MATLAB, which is the standard tool for technical calculations at the Royal Institute of Technology.
-Here, with one and the same basic setting, I can quickly find out what takes place if material, dimension, voltage,
and anything else is changed, explains Thorbjörn Ebefors.
-We can accordingly avoid many prototype stages and anything else is barely possible on economic and time grounds.
There are several good programs for finite element calculations. In the majority of them, however, the thermal expansion is calculated first and then the result is inserted in a module for strength and so on. COMSOL Multiphysics, on the other hand, takes account of all phenomena simultaneously, which makes the modeling process considerably faster and simpler. In addition, the price is usually lower.
Modeling of the micro-robot's leg is achieved simply in COMSOL's graphical user interface. The V-shaped fillings consist of temperature-sensitive plastic. When the plastic is expanded, the leg that makes it possible for the robot to move is bent.
Multiple "what-if" analyses
The robot moves at 1 mm/sec, carrying 50 times its own weight.
The hinge in this project has been developed step-by-step by means of simulation and FEM calculations. By testing different material properties, the researchers were able to arrive simply at which material should be used in the joints, how many joints are needed for a given movement, and how self motor activity should be activated. Without a tool such as COMSOL Multiphysics, it would not have been possible.