Considerations in Designing ‘Fail-Safe’ Motor Drive Circuits

Consider, for just one moment, the ability to monitor human brain activity at its source. Imagine the knowledge that could be gleaned by directly observing the non-stop electric symphony composed and conducted by a 120 billion-piece neuronal orchestra.
 
Fancy gaining a ringside seat to this cerebral concerto, without the need for big, bulky machines, strange-looking skull caps, or long, tangle-prone wires. A tiny, perhaps flexible, electrode would suffice as the entrance fee.
 
To truly witness the magical harmony of the brain’s electric oscillations, that electrode would have to be extremely small—conceivably, 100 nanometers or so (roughly 1,000 times thinner than a human hair).
 
Creating an electrode of that size certainly is technologically possible. Medical electronics have steadily been shrinking over the last two decades as digital health and minimally invasive surgical procedures spawned a worldwide thirst for smaller, more complex computerized devices that improve diagnoses and tracking. The scramble for diagnostic tests, personal protective equipment, ventilators, and other medical supplies associated with the planet’s battle against COVID-19 is expected to increase demand for medical electronics over the next seven years.
 
Medical Product Outsourcing’s September feature, “Mission Complete,” details the various trends and challenges currently shaping the custom medical electronics market. Bob Kish, sales manager at FAULHABER MICROMO LLC, was among the experts interviewed for this story. His full input is provided in the following Q&A:
 
Michael Barbella: What factors must be taken into consideration when designing electronic components for medical devices?
Bob Kish: Motor drive circuits must be “designed to fail” in a safe manner to protect both patients and physicians. For example, a run-away motor on an infusion pump could result in a patient receiving a lethal dose. This same situation, in a surgical power tool for example could cause damage to a patient’s internal organs or injure the physician’s hand if excessive torque is produced instantaneously. Fail-safe motor drive designs are particularly important for Class II and III medical devices like these.
 
Barbella: Please discuss some of the challenges in designing and manufacturing electronic components for medical devices. How has your company overcome these challenges?
Kish: Medical device applications typically have many design constraints which are in some cases conflicting. Creating system-level performance and thermal models allows us to optimize critical parameters and see the effects of our optimization efforts. These models help us customize motor windings and gearhead ratios in order to match performance to the customer’s precise design parameters. Our ability to offer a wide range of system-level solutions based on coreless DC, brushless, stepper and piezo motor technologies allows us to propose multiple solution scenarios, each with different trade-offs to assist device manufacturers with their design optimization and selection process.

Barbella: What are customers demanding or expecting in their electronic components?
Kish: Device manufacturers are looking for motion component suppliers that are capable of providing fully-integrated, system-level motion solutions that incorporate additional components, such as machined parts, precision lead screws, gears, pulleys, bearings, drive electronics, sensors and interconnect PCBs. This approach simplifies the supply chain, reduces inventory, and improves quality for the customer.
 
Barbella: How is the trend toward miniaturization of medical devices driving the design of electronic components? Please explain.
Kish: We’re definitely seeing a trend in the need for higher torque and power densities in order to push the performance envelope or to shrink the size and weight of devices—particularly with hand-held and ambulatory devices. Demand for IoT devices is growing rapidly and many of these are hand-held devices used in a point-of-care environment, so battery life, weight and size become more important design considerations. Fully embedded and integrated motion solutions can also help reduce component count while also reducing the overall size of the end product.
 
Barbella: The industry has grappled with a worldwide electronic components shortage in recent years. What solutions are available to tackle this problem?
Kish: At FAULHABER, we source our own proprietary ICs whenever possible so we’re not competing with demand from other, larger players in the market, and to further ensure quality of our drive solutions. In a case where this is not possible, then we may carry up to 12 months of component inventory to ensure we’re able to respond accordingly, when needed. This strategy allowed us to help a number of medical device and diagnostic equipment manufactures ramp up production to meet the increased demand created by the COVID-19 pandemic.
 
Barbella: How does your company tackle electronic components shortages and parts obsolescence?
Kish: We have a robust Change Management System implemented across all of our FAULHABER facilities, both in Europe and in the U.S. that identifies these risks as early as possible and allows us to develop mitigation strategies before they become a problem or impact our customers’ production schedules.