Model-based design aids medical device test
Rick Nelson, Editor in Chief -- Test & Measurement World, 2/1/2010 2:00:00 AM
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Engineers can save themselves a lot of effort by carefully evaluating their designs in software before building hardware. Model-based design can be of significant value in helping isolate domain experts, such as medical-device or aerospace engineers, from the need to understand low-level hardware and software details.
Brett Murphy, manager of technical marketing at The MathWorks, recently made the case for early verification (Ref. 1). He said that aerospace and automotive members of the company's customer-advisory boards cite verification and validation as top priorities. Errors most often emerge at a project's specification stage, and fewer errors manifest themselves during design, implementation, and test. But engineers frequently don't detect the errors until the test stage.
One MathWorks customer that has employed model-based design is the Cleveland FES Center at Case Western Reserve University, which develops technology that can restore movement to individuals with neuromuscular disabilities. Robert Kirsch, PhD, a professor of biomedical engineering at Case Western Reserve and associate director of technology at the Cleveland FES Center, said that adopting model-based design reduced the development time of FES (functional electrical stimulation) devices and enabled researchers to build customized prototypes for patients many times faster than they could before.
Traditionally, Kirsch said, the organization has relied on a group of software engineers who wrote low-level assembly and C code to implement algorithms, safety features, and system checks specified by the systems-integration team. A successful implementation, he said, would take several iterations and would constitute a bottleneck, but model-based design tools allow programming to occur at a higher, block-diagram level, allowing engineers and clinicians to modify an FES controller application and immediately test the results.
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design, simulation, and operation details The MathWorks (www.mathworks.com) announced last fall that the Cleveland FES Center (www.FEScenter.org) is using MathWorks tools for model-based design to reduce the development time of FES (functional electrical stimulation) devices and enable researchers to build customized prototypes for patients many times faster than they could do before. Specifically, the center used the tools to help develop a UECU (universal external control unit), whose modular software and hardware design enables research engineers to modify an FES controller application and immediately test the results. Robert Kirsch, PhD, a professor of biomedical engineering at Case Western Reserve and associate director of technology at the Cleveland FES Center, explains that to restore movement to paralyzed arms and legs, FES devices send small electrical currents to electrodes—implanted in the body, worn on the skin, or operating through the skin—in a coordinated way to enable a patient's limb to move or hand to open and close. Adapting the FES device for each patient was a time-consuming process, as the device software needed multiple iterations for a customized response to each patient's needs. Adding to the complexity, Kirsch says, are the variety of applications FES can serve: it can restore hand and arm function, provide posture control for standing, walking, and sitting, and it can control bladder or swallowing function. Tailoring an FES system for a patient, he says, requires an interdisciplinary team, typically including a PhD, an engineer, a physician, a surgeon (for implanted devices), and an occupational therapist (who is involved in patient training and functional assessment of the results). He adds, "We also have a team of engineers and technicians who design the stimulation systems and the electrodes and who write the embedded software for the control of the devices." With MathWorks tools, teams are able to develop, test, and implement algorithms that suit specific patient scenarios, reducing the traditional development cycle for some FES functions to less than a day. "All of our FES applications used to be built by dedicated programmers using C code," says Kirsch. "The overall process was slow because everything had to be done by our central programmers, which limited how quickly we could move from idea to implementation. MathWorks tools for model-based design provide the flexibility and ease of use that enables our clinical groups to develop and refine FES applications on their own." The UECU project involved a range of MathWorks products beyond Matlab and Simulink, including Signal Processing Blockset, Stateflow, Real-Time Workshop, xPC Target, and xPC Target Embedded Option. More than 30 UECUs are currently in use by patients today, the center reports, and over the next decade, the center plans to introduce a new technology that is a fully internal system, inside the body. Lab prototypes of the new system are already running programs created with Simulink and Real-Time Workshop the center reports. —Rick Nelson |
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