Tomorrow ' s Surgery : Micromotors and Microrobots Anita

Surgical procedures have changed radically over the last few years due to the arrival of new technology. What will technology bring us in the future? This paper examines a few of the forces whose timing are causing new ideas to congeal from the fields of artificial intelligence, robotics, micromachining and smart materials. Intelligence systems for autonomous mobile robots can now enable simple insect level behaviors in small amounts of silicon. These software breakthroughs coupled with new techniques for microfabricating miniature sensors and actuators from both silicon and ferroelectric families of materials offer glimpses of the future where robots will be small, cheap and potentially very useful to surgeons. In this paper we relate our recent efforts to fabricate piezoelectric micromotors in an effort to develop actuator technologies where brawn matches to the scale of the brain. We discuss our experiments with thin film ferroelectric motors 2mm in diameter and larger 8mm versions machined from bulk ceramic and sketch possible applications in the surgical field. A.I. Laboratory Working Papers are produced for internal circulation, and may contain information that is, for example, too preliminary or too detailed for formal publication. It is not intended that they should be considered papers to which reference can be made in the literature. 1 Intelligent Machines Today surgeons routinely remove organs with minimally invasive procedures that were unheard of just a few years ago. What will be next? It seems clear that more dextrous manipulators and better visualization tools will be the upcoming items on the agenda. After that, perhaps placing the intelligence also at the point of interest? While the idea of an autonomous robot running amuck inside the human body is a scary thought, it certainly is plausible to imagine beginning with low level reflexive actions for locomotion or manipulation carried out autonomously, while a fiber-optic cable is tethered to a surgeon for observation and direction. At the MIT Mobile Robotics Laboratory, new approaches in artificial intelligence have led to novel intelligence architectures used on robots which explore, build maps, have an onboard manipulator, walk, interact with people, navigate visually and learn to coordinate many conflicting internal behaviors [1]. This type of control system, known as a subsumption architecture, is implemented as a distributed layered network of augmented messagepassing finite state machines [2] and enables very tight loops between perception and action to be maintained in a mobile robot's dynamically changing world. Figure 1 illustrates Squirt, the smallest simplest robot built under this paradigm [3]. Two microphones and a light sensor trigger insect style behaviors of hiding in the dark and moving towards noise. The subsumption program endowing Squirt with these capabilities fits in a very lean 1300 bytes of code. Unfortunately, Squirt's lone DC gearhead motor grants only one degree of freedom; forwards or back and turn (when a clutch on the rear axle allows one wheel to slip). While an entire computer with accompanying software, sensors and batteries can fit into a Squirt-sized package, it is difficult to include very many motors for finer dexterity. With the advent of silicon micromachining techniques in which electrostatic motors the size of a human hair can be etched in place on the surface of a silicon chip [4], the thought arose to pattern an entire robot on a chip [5]; sensors, subsumption control system compiled to the gate level, actuators and solar cells, as all components could be fabricated in silicon. Resulting machines could be printed in the same manner as integrated circuits and mass produced in low cost batch fabrication lots, enabling cheap disposable robots. Unfortunately, the problem here is that silicon electrostatic motors have a number of drawbacks for small robots. They typically spin at high speeds with very small torque and are hard to scale up, necessitating that the rest of the system be scaled down to their domain. We would be interested in slightly larger, but still small motors which would be compact, directdrive, cost-effective and able to couple useful torque to a load for the purpose of creating robots that act as autonomous sensors and manage to find their way into hard to reach places. A number of technologies look promising here such as magnetic or electrostatic wobble motors [6], polymer gels for artificial muscles [7] and piezoelectric ultrasonic motors [8]. Our investigations are focused on scaling down ultrasonic motors and attempting to microfabricate them using new ferroelectric thin films of lead zirconate titanate (PZT) [9]. Figure 1: Squirt is an autonomous robot measuring 2.5cm on a side, carrying onboard computer, sensors, motor and batteries. No.-vdlakil Motar enmories Srai nuaes