Future designs will include additional of degrees of freedom to permit the insertion and rotation of cannula and stylet. The WPI robot consists of one module with X, Y, Z translation and two rotational modules that correspond to the arc angles of a head frame. Because one set of legs is the always in contact with the actuator at any time, they are inherently safe actuators (providing braking when unpowered) with the motors provide a stall force (holding force?) of up to 10 N. In practice, they are driven in alternating pairs (see figure 3) so that they “walk” a drive rod forward in nanometer steps at speeds as high as 15 mm/s (or spin a disc in the case of rotary motion). The units consist of a set of bimorphic drive legs that are constructed so that under an applied voltage, they flex slightly and extend (see figure 2).įigure 2: PiezoLEGS® motor (bottom) consists of bimorphic piezo ceramic legs (top) that respond unequally to an applied voltage. The WPI team found the solution in the PiezoLEGS motors from MICROMO. The problem is that the displacement introduced by the piezo effect is only a fraction of a percent of component size, while the MRI robot required up to about 100 mm of linear travel or a continuous 360 degree rotation. Piezoelectric actuators are based on a piezoelectric ceramic that expands under an applied voltage. The answer proved to be a piezoelectric device. It was obvious from the outset that the MRI robot had to be based on non-traditional actuation. The powerful magnetic field generated by an MRI machine makes hazards of even small ferromagnetic objects like screws, let alone, motion devices like permanent magnet motors, gearboxes, and actuators. In the case of the MRI robot, Fischer’s team faced another enormous challenge delivering all of these characteristics in a system that can also function in multi-tesla magnetic fields. Systems need to be accurate and repeatable, with ultrahigh resolution. The process of designing surgical devices is rife with challenges. Results: WPI team has built a system that promises to revolutionize the treatment possibilities of MRI. Solution: Use sophisticated controls, engineering and piezoelectric positioners from MICROMO. Institute Industry: Medical Robotic Surgical ToolsĬhallenge: Design a surgical robot designed for use inside an MRI machine that can operate within the high magnetic fields generated by an MRI. (Courtesy of Worcester Polytechnic Institute) Of course, building a robot that can operate within the high magnetic fields generated by an MRI unit was not easy, but with sophisticated controls engineering and piezoelectric positioners from MICROMO, the WPI team has built a system that promises to revolutionize the treatment possibilities of MRI.įigure 1: Surgical robot uses piezoelectric motors to operate in the high magnetic field of an MRI machine. Guided by real-time feedback, the robot can position a high-energy, interstitial focused ultrasound probe exactly at the tumor, delivering optimal surgical results and an ideal outcome for the patient. Today, Worcester Polytechnic Institute professor Greg Fischer, is busy developing a surgical robot designed for use inside an MRI machine (see figure 1). Surgeons treating brain cancer face a conundrum: They can capture ultra-high-resolution images of the tumor using magnetic resonance imaging (MRI) or they can use ultra-precise surgical tools to remove the tumor, but they can’t do both at the same time.
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