Fibroids affect more than 30% of women in the U.S. according to the Jones Institute for Reproductive Medicine at Eastern Virginia Medical School in Norfolk. The good news is that yesteryear's devices of choice — monopole loop electrodes that scraped tissue from uterine walls, while producing large amounts “chips” that slowed and impacted the accuracy of the operations, have been replaced with less intrusive devices, a longtime request of physicians.

Even better news has to do with an important upgrade made possible by device maker Interlace Medical, Framingham, MA, and its motor supplier Maxon Precision Motors, Fall River, MA .

A 2½-year, five-man engineering team effort at Interlace Medical has resulted in the MyoSure tissue removal system. The effort addressed and met the challenge of achieving speed, accuracy, and cost effectiveness in a non-invasive device. Interlace's first version used an autoclavable motor manufactured by Maxon Precision Motor. The device used a single motor mounted inside the handle, with all the electrical connections transferred through a tiny cable.

The latest version of the MyoSure system was designed with the same cutting technology, except that the motor is now housed inside the controller chassis instead of the probe, eliminating the need for an autoclavable motor. This not only reduces the costs associated with having to buy autoclavable motors, it also reduced the size and weight of the handheld device, making it easier for a doctor to manipulate. An integral rotary encoder is used for closed-loop control of the motor. Still, because the enclosure for the MyoSure had already been designed, the company had to find a compact motor with the highest performance per size that they could get.

The MyoSure operates from a foot petal and only turns in one direction, which made motor selection easier. The RE40 motor (40mm diam × 71mm length excluding shaft) used in the device is fitted with rare-earth magnets to provide its high performance while maintaining a compact size. These motors use a patented rhombic moving coil to deliver long life, low electrical noise, fast acceleration, and high efficiency. These signature high-performance characteristics of Maxon motors are due to the relatively low inertia of the rotor, small diameter commutator, tightly toleranced air gaps, unique brush design, and extremely low brush arcing. design Plus the component's ironless rotor allows for zero cogging over 7.5Nm of torque and simple, accurate control. Motor efficiency is 86% depending on the winding.

Interlace designed a unidirectional flexible shaft into the system that interconnects with the remotely located Maxon RE40 motor. This approach meant that it could go to a single-use, disposable probe system, which helped with certification. The MyoSure has obtained FDA 510[K] clearance and expects CE Mark certification to sell in Europe in the next year.

The device and its optical scope are 6.25mm in diameter. This means that patients require less anesthesia during the operation. Overall, the device can provide a clear operative field, fewer device insertions, reduced perforation risk, and shorter procedure time — which was the primary design goal.

The MyoSure incorporates Maxon's EPOS 24/5 position controller as the driver for the device. By working closely with Maxon engineers from day one of the project, Interlace was able to avoid “overdesigning the device, which would have increased our production costs,” says Interlace Vice President or R&D Albert Chin.

EPOS 24/5 is a digital motion controller capable of being used in position, velocity, and current mode. It communicates through RS-232 or CANopen communications protocols. Software for CANopen and Windows DLL is complimentary. The controller only requires an 11 to 24 VDC input to be capable of operating at a max of 5 amps continuous current and 10 amps peak current. The 50 kHz switching frequency and built-in choke ensure compatibility with most low inductance motors, while the sinusoidal commutation for brushless motors ensures minimal torque ripple and low noise.

The EPOS controller uses simple logic and control functions for monitoring the motor's operation, including acceleration and deceleration, as well as speed. The motor control logic is a software program that is burned into firmware at the factory. The MyoSure control box has passed all the electrical safety testing necessary for Class B office use.