Motion Control Resources
Medical Market Presents Opportunities for Motion
by Kristin Lewotsky, Contributing Editor
Motion Control & Motor Association Posted 09/02/2008
Healthcare is a multibillion dollar industry and motion control definitely has a piece of the pie. Whether the application is research, such as DNA testing; therapeutics, such as insulin delivery pumps; or logistics, such as hospital bed positioning; motion control plays an important role throughout the industry.
Although disposability is king in the patient care markets, cost and electronic waste regulations tend to relegate motion control components to devices that can be sterilized and reused. It’s an effective approach but it creates challenges. Moisture alone can wreak havoc on improperly designed precision motors. The autoclaves that perform sterilization use steam to raise items to a temperature of around 121 deg C at 15 psi for 20 to 30 min. Such conditions can degrade even the most robust devices.
As always, the application determines the solution. If cost is paramount, one approach is to add an enclosure and a shaft seal to a standard motor to block out moisture. For an application with only limited sterilization requirements, this could be an economical alternative. The problem is that even the best seals have limited lifetimes. Once they’ve gone through sufficient autoclave cycles to be degraded, moisture will almost inevitably enter the motor. How long the unit lasts after that point depends on where the water vapor penetrates. For applications that need many hundreds of autoclave cycles, a better attack is to use a motor that’s designed for sterilization, or even start with that unit and add seals.
Design of an autoclavable motor is no easy feat. “Generally the magnet has to change, the lubrication has to change, the type of winding, the type of housing,” enumerates Paul McGrath, sales engineer at Maxon Precision Motors (Fall River, Massachusetts), which supplies motors for applications like infusion pumps and surgical and dental handpieces. Although demagnetization can be a risk at autoclave temperatures, the bigger concern is corrosion. “We generally use neodymium magnets for non-sterilizable applications, whereas we’ll use samarium cobalt magnets for sterilizable applications,” he says. The technology doesn’t come cheap, of course. An autoclavable motor can run as much as twice the cost of a conventional component. For the right application, though, it’s worth it -- a motor rated as autoclavable is typically designed to survive 1000 autoclave cycles.
In the case of Linak U.S. Inc. (Louisville, Kentucky), which produces motion systems for powered hospital beds and patient platforms, moisture presents a different problem. “It’s not so popular in the United States, but in Europe they actually run the beds through a big washing machine that looks like a dishwasher,” says L. Robert Tupman, director of sales support at Linak U.S. The company tends to use DC motors, both because of reduced noise, reduced overall system weight, safety and because they’re compatible with battery back ups. Of course, the devices need to meet ingress protection standards, but Linak takes additional precautions. “In some of our products, there are sensors inside the control box housing itself and if it senses water inside that box, it'll set an alarm off,” Tupman says. The use of rod-style actuators simplifies the task of sealing, and the actuator designs incorporate stainless steel rods and powder-coated steel housings.
Electromagnetic interference (EMI) is a perennial issue in motion control, but especially in the medical market, with its widespread telemetry and instrumentation. The first line of defense is good cabling practices, focusing on proper shielding, grounding and design of cable runs. Filtering is another method to control EMI. Low-inductance motors with ironless cores drop noise even further, McGrath notes. “The motor is built around a permanent magnet,” he says. “A rotating coil fits in a tiny air gap between the magnet and housing, and the housing closes the magnetic path. Basically, the motor is ironless on the inside, which yields very low inductance and low inductance means very low EMI.” The use of different brushes -- precious metal versus graphite, for example – reduces EMI even further.
Standards and regulation
Of course, any sort of patient care brings up the specter of regulatory bodies like the U.S. Food and Drug Administration (FDA) and their approval processes, which can be onerous, at best. There was a time that FDA approval was the headache of the OEMs, not the motion suppliers, but no longer. These days, McGrath says, customers are happy to share the pain. “There are definitely some more stringent requirements coming from customers, and some of that we’re now starting to see passed back to us in terms of approvals and standards to be met,” says McGrath. Maxon has tackled the challenge by establishing a medical division tasked specifically with addressing issues like traceability and serialization of part numbers to aid in compliance.
Linak considers approvals part of their value proposition. “One of the things we do to help make our customers lives easier is to have our systems certified to the medical standard that our customers would have to meet,” says Tupman. These are not FDA standards so much as approvals from Underwriters’ Laboratory (UL), the Canadian Standards Association (CSA), or Japan’s National Institute of Advanced Industrial Science and Technology (AIST, previously the Electrotechnical Laboratory (ETL)). “We go ahead and make sure that our products are compliant with those standards as far as the actuator systems and electronic components,” he says. “We get the approval; we actually have UL file numbers or ETL file numbers on the bulk of our products.”
Perhaps a bigger issue than approvals is that of liability. “We take a very conservative approach here because the consequences are so dramatic,” says Ty Safreno, CEO/CTO of Trust Automation (San Luis Obispo, California). The company supplies components and systems to industries such as semiconductor manufacturing and biotech, but only occasionally dips into the medical market, primarily because of concerns about insurance burdens. Certainly, the company that actually sells a medical device is the one that must seek FDA approval and is accountable in the case of failure, but liability has a way of spreading around. For Trust, controlling exposure is a key part of their business strategy.
“The go/no-go gauge for us in this industry is whether or not we’re on [the customer’s] insurance rider,” says Safreno. “For laboratory machines, the insurance part is very reasonable. When you get a patient involved, it gets crazy.” It can take years to get a device to the approval stage, let alone through it, and that’s just the start. “If [a customer] puts out a medical device during the beta phase or testing phase, we’re stuck with carrying the insurance for that for the foreseeable future. We have not been willing, as of yet, to sign up for that level of commitment in that industry,” says Safreno. “If we’re covered by [the customer’s] insurance, then we’ll sell our device to them.” As another strategy to minimize liability, Trust avoids customizing components and systems for customers in these markets.
Motion control has much to offer the medical sector and the medical sector provides a wide range of opportunities for the motion control industry. The challenges, however, are undeniable. For suppliers to carve out a piece of this market, they need to choose applications that fit their technology, understand the challenges, and craft a strategy for dealing with the pitfalls. Companies that do these things are positioning themselves for success.