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Edited by Stephen J. Mraz
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Accurate, repeatable positioning is crucial to a host of medical devices — everything from CAT scanners to blood-testing equipment to milling machines for lenses. And motion must often be in more than one axis. Fortunately, advances in ICs have led to better, more-reliable motion controllers. Here are four such biomedical advancements.
Machining new eyes
Cataracts affect patients of all ages, but hit senior citizens the hardest. In fact, cataracts are the leading cause of vision loss among adults age 55 years and older. And when medication and extremely strong glasses don’t rectify the problem, physicians surgically replace the scarred natural lens with an artificial one made of plastic.
Most firms making these interocular lenses invest about $240,000 for a line of lathes and milling machines. That gave Gary Goins, president of IOL International of America, Largo, Fla., an idea. He combined all the machining capabilities needed to turn out high-quality interocular lens into a single machine he dubbed the Optical Generator. It costs about one-third the price of the separate machine tools that make the same lenses.
The new machine uses a single X-Y table with motion handled by a Galil DMC-1832 three-axis PCI bus controller. “The controller provides precise 0.1-micron resolution, and the smoothness of the motions let us cut optics in less than 45 seconds per side,” says Goins. “The same holds true for milling.”
The DMC controller also streamlines and simplifies operations. For example, the Optical Generator uses AutoCAD to draw lenses, then the controller’s translator converts the DXF CAD files to a DMC program. “The controller also interpolates linear and circular motion for precise X-Y motions, simple and accurate PID tuning of the high-resolution linear encoders, and a user-friendly interface,” says Goin.
The compact Optical Generator consists of a tray which holds carriers for lens blanks, a 30,000-rpm lathe, an air-bearing spindle for machining lenses, and an air-bearing profile-milling station that puts fasteners or connectors on lenses. These fastening features hold the lens in the center of the patient’s eyeball. The machine cuts both sides of the lens in 30 min. Conventional methods require a time-consuming changeover from one machine to another. The Generator can create interocular lenses, as well as ophthalmic implants and other medical devices that require small, precise parts.
Ready, aim, . . .
Oncologists and surgeons have known for years that radiation can kill cancer cells and tumors. But it also kills healthy tissue. That means precisely aiming the radiation is critical. And to make aiming more difficult, target cells are often deep in the brain or surrounded by healthy tissue, and they can shift in position over time.
To ensure patients get the right dose in the right places, engineers at TomoTherapy, Madison, Wis., added a CT scanner to its radiation-delivery platform, the Hi-Art treatment system. Both mount on a gantry that rotates 360° around a patient, who lies on a table during treatment. This lets tens of thousands of intensity-modulated radiation beams take several paths to the affected tissue, and each beam contributes to the total delivered dose. Technicians check targeting against real-time CT imaging to ensure radiation is accurately aimed.
Keeping the table and patient stable is a key factor in Hi-Art’s accuracy. A Galil DMC-2153 five-axis controller holds the table to ±1 mm in three axes. TomoTherapy hopes to push this accuracy to submillimeter levels in the near future. The unit’s PID Compensation feature handles the Z axis (up and down). A built-in motor and stepper drive works with the DMC-2153 to control the Y axis (in and out of gantry bore) and X axis (right and left).
The controller uses two types of feedback, incremental and synchronous serial-interface (SSI) absolute, to confirm and maintain table position in case of a disruption due to power loss, and to precisely synchronize the X and Y axes.
“We considered several motion controllers for the Hi-Art system, but Galil’s met our requirements for Ethernet control of stepper and servomotors, the ability to multitask, and SSI feedback,” says TomoTherapy Research Engineer Graham Reitz. “The controller also had to be compact enough to fit in a small space.”
TomoTherapy engineers made good use of the controller’s I/Os, after Galil customized it to accept all SSI devices for feedback. For example, some I/Os handle tasks such as machine shutdown, clutch status, and emergency stops. The controller also sends signals to its own embedded computer to perform motion calculations while Hi-Art’s Linux computer calculates, coordinates, and talks directly to the controller to provide redundancy and increase safety.
A device being developed at Focus Surgery Inc., Indianapolis, the Sonablate 500, uses high-intensity focused ultrasound rather than radiation to destroy cancer cells in prostrate glands. It uses a transrectal probe that houses both an imaging transducer and an ultrasound emitter to treat several areas on the gland during the same 2 to 3-hr session.
A Galil DMC-1822 two-axis PCI controller aims the emitter and imager, focusing to a point the size of a grain of rice. The probe is swept back and forth across the target area to destroy the cancer cells. The controller provides the speed and accuracy for this exacting treatment. For example, it can maintain positional accuracy to within 0.1 mm. And for the imager, the controller handles four 45-mm longitudinal moves and six transverse moves per second. The controller can also store a 1,000-line program and still run complex move profiles and programs.
Streamlining the lab
Medical research and diagnosis involves mountains of lab work, which used to employ thousands of technicians handling test tubes filled with samples. But the human factor leads to misidentification, contamination, and costly errors. As a result, a host of companies are trying to automate medical labs. NGNY Devices SL, Barcelona, for example, developed their STDK500 Automatic Sorter Decapper to sort and uncap sample tubes, then organize them in trays compatible with analysis equipment.
The device’s robotic arm takes a tube from a tray, positions it so its bar-coded label can be read, then places it on a conveyor. The bar code includes information on which tests samples are to undergo and whether the tube needs to be decapped. The conveyor stops at a decapping module where tubes that must be decapped are opened. Next, a second robotic arm places the tube in the proper tray for transport to specific test stations.
The Sorter Decapper relies on Galil’s DMC-2183 eight-axis motion controller to handle both robots’ motion. Axes one through four control the first robotic arm, while axes five through eight handle the second arm. A pair of Galil AMP-20440 four-axis 200-W servodrive boards attached to the controller, will save space and reduce wiring and costs. A DMC-2143 four-axis Galil controller with a single AMP-20440 board maneuvers the decapping module.
“We programmed the host PC and used Galil’s .NET API command software to communicate with the controllers over Ethernet,” says John Viladomat, design engineer at NGNY Devices. “We also have application programs burned in the controller’s nonvolatile memory, and the host PC executes them depending on the state.”
The current STDK500 handles 500 tubes/hr, but the company can expand the device and add new modules. “For example, it would be easy to add a recapping module controlled by another Galil Ethernet controller,” says Viladomat.