Brushing Aside an Old Style of Medical Device Motors

Author: 
Chris Newmarker and Brian Buntz

MedTech designers turn to brushless dc motors for their quieter, more precise traits.

New applications are resulting in new needs—as well as innovation—when it comes to medical motors.

The workhorse has long been the brushed direct current motor, economical but also in need of maintenance because parts wear down due to friction.

But hospital administrators now want to increase efficiency and reduce workers compensation claims through diagnostic equipment that runs quieter and can easily be moved around the facility. Blood and DNA analysis machines that are proliferating also require quieter, super-precise motors.

Brushless dc motors, sometimes called direct drive motors, are all of a sudden in demand.

“If I look at it, in terms of the medical market specifically, the trends that we are seeing are based on two areas. They relate to quietness of operation and energy efficiency,” says John Morehead, national sales manager for Crouzet Motors at Custom Sensors & Technologies (San Diego, CA; www.crouzet.com).

Morehead thinks it is mostly about mobility when it comes to brushless dc motors.

“The brushless motors are typically designed to work from low voltage,” Morehead says. “Anywhere you are going to have battery power or low voltage in a hospital or operating room environment, it is a good environment for brushless dc motors. And then the other thing that we are seeing is the move to greater mobility of a wide variety of functions in the hospital.”

Kollmorgem AKMH
Kollmorgen has its brushless stainless steel AKMH Servomotors that are meant to have a long life even with daily exposure to chemicals and high pressure wash downs. 

Brushless dc motors are already widely used in diagnostic equipment such as CT-scan type equipment, and equipment related to opening protective barriers in medical environments such as an x-ray room.

Morehead, though, suspects there also is a growing demand when it comes to mechanizing activities that used to be done by hand in hospitals, and staving off workers compensation claims related to shifting around equipment that is heavy or cumbersome or moving heavy patients.

“This might include taking someone from the gurney and moving them onto the bed in the room,” Morehead says.

“By having a motorized way of doing it, it is easier and more flexible,” Morehead says.

The demand has resulted in medical motors innovation: “What we are seeing from the motors side is an interest in more power dense motors so you can get higher torque from either the same size package or a smaller package. That continues because people are looking at trying to reduce the overall package size of equipment,” Morehead says.

Making Better Motors for IVD

More precise in vitro diagnostic testing is also increasing demand for brushless dc motors, says John Garrity, marketing manager at Kollmorgen’s Dover Motion business in Boxborough, MA (www.kollmorgen.com). Garrity specifically spoke about direct drive linear motors, an area where Dover has seen increased demand.

Direct drive motor technology has been around for awhile. “But it’s starting to get more popular with medical applications. The size of particles are getting smaller. Typically, people used to get by with belts and screws with the motion, but the higher accuracy is driving people to direct drive motors,” Garrity says.

“They’re a lot quieter than a traditional ball screw or leadscrew drive. So it’s not noisy for the lab equipment.”

The latest DNA sequencing and blood hematology machines need to precisely move samples slides on x and y axes, as well as vertically move an objective lens focused on the image of the blood cells or the genes.

“It’s pretty neat stuff. You’re talking about microns here. The parts that are being inspected are anywhere from 1 micron to 5 to 10 microns,” Garrity says. “You can get much better accuracy positioning samples with the direct drive solution. … You get friction when you’re turning a screw. … With direct drive, there’s no friction there. There’s no contact.”

The motors themselves generally run around 2-by-4 in., and they need to be fairly flat.

Integrating Controls and Helping the Environment

Integral intelligence is another important development when it comes to motors, Morehead says. “This trend will enable customers to focus more on the control technology that is specific to their medical equipment rather than having to get into the control technology just to turn a motor shaft.”

The extra cost for such integral intelligence is also diminishing, In fact, Morehead thinks it can save money.

“By integrating the control electronics into the motor package, you have a significant savings in cost. In terms of installation costs, you don’t have the cost of wires and cables and connectors and the potential problems of having a separate control,” Morehead says.

“Now you have brushless motors that can have a simple variable speed control built in where you have variable speed control built in. And then you can also have what is really an intelligent brushless motor that would have built in positioning control so you would be able to use a computer with some fairly simple, intuitive software to program the move profiles that you want … in the motor.”

There is strong interest in motors that are able to meet higher environmental protection requirements such as IP69K, which requires the ability of a product to hold up against extreme washdowns using harsh solvents and elevated temperatures.

“Long service life is another growing desire,” Morehead says.

Keeping the Brushed DC Motor Relevant

While brushless dc motors are trending in medical device circles, Morehead is actually excited about Crouzet Motors’ low-noise brushed motors.

“In some cases, customers had been thinking about using a brushless motor in order to reduce noise of equipment, but with this low-noise brushed, they can use that. And it is less expensive and simpler to control. What we have found is in that designing the motor to reduce the noise, it also has significant other benefits,” Morehead says.

“The brushed dc motor is desirable because it is economic and relatively power dense. The control for it is very simple and very cheap. And they are easy to design into equipment.”

Morehead didn’t go into too much detail in explaining how the company developed low-noise brushed motors, but he said Crouzet Motors reduced motor noise through material choices and the precision in which the motors are assembled. “Basically, it is a motor that is much more highly engineered and produced in a much more precise environment than is typical,” Morehead says.

How to Choose

When it comes to choosing the right type of motor, Morehead suggests getting engaged early on with a motor company’s application engineer.

Maybe the choice is that you are looking at getting a certain speed and a certain torque and you know you are going to have a certain input voltage. “But if you are able to work with the application engineer, you can perhaps get a variety of prototypes that can be tested—either brushed or brushless motors. I think that when you are able to do that, you are able to make more intelligent choices than if you are only looking at one possible situation to do it,” Morehead says.

“We’ve had customers who have had started out looking only at a brushless motor with a right angle gear reducer and, in a relatively short period of time, have changed to using a more economic brushed motor with a parallel shaft planetary gear reducer.”

Problems with motor selection often occur when devices have already been mostly designed before a motor supplier is contacted, or when shortened timelines rush the process. “Where the real problems occur is when somebody has designed most of the device and then they decide to call in the motor supplier and say what do you have that can fit in here and produce the output that we are looking for,” Morehead says.

While it is true that product development timelines have been crunched in recent years, medical devices with motors in them require special scrutiny. “If you are able to look at the motor being what is really going to be doing the work in whatever you are designing, it becomes very important to see that you address that early on in the design phase,” Morehead says.