One of the growing problems facing nurses is a reduced staff, and with it the need to care for overweight patients with very little help. This effort has led to musculoskeletal disorders (MSDs) including back injuries. In fact, 12 percent of nurses leave the profession each year due to back injuries. Those working in nursing homes have an even higher rate of injuries. Until recently, moving a patient was performed manually or with minimal automation.

This 3D CAD drawing of the PowerNurse shows how thin the final product was required to be in order to slip comfortably under a patient.
Allowing a single nurse to safely and comfortably transfer a patient without risk of injury required a fully automated device. Astir Technologies (Concord, MA) used the latest technologies available to provide patient transfer in a manner that decreases hospital costs and reduces injuries to health care professionals, while minimizing the discomfort to the patient. With this in mind, the company designed and manufactured the PowerNurse™.

All of the mechanisms are packaged in a low-profile assembly that rides over a standard hospital stretcher. With the PowerNurse, patients can be moved among hospital beds, stretchers, imaging equipment, operating room tables, and exam tables. According to Chris McNulty, Astir Technologies President and developer of the PowerNurse, “Other less expensive friction-reducing devices decrease but do not eliminate the risk of nurse injury while performing a lateral transfer.” A critical area evident in the device’s design is that of the motors and gearboxes. High-power rare earth magnets and advances in motor winding have resulted in high-torque motors in small packages.

McNulty’s solution involves a series of conveyor belts, motors, and electronics that fit into a thin profile that allows the transfer of very heavy weights automatically. During development of his first prototype, over 400 pounds was easily transferred using one-fifth of the capacity of the 250W Maxon EC45 motors designed into the device. This meant that the 120W ECmax 40 motors could be used in the PowerNurse, while the larger EC45 motors could be used for a bariatric model in development. Originally, the PowerNurse traveled at only one speed (1 inch per second). Although this speed was fine for patient pick-up and delivery, it was too slow for the lateral transfer process. So, McNulty incorporated a two-speed option into his beta model, where the device operated at 1 or 2 inches per second.

The PowerNurse incorporates four ECmax 40 motors; four GP 42C, three-stage, 43:1 gearboxes; and four DEC50/5 servo-amplifiers along with a 400W, 48-VDC power supply. A specific challenge in the development of the device concerned the drive rollers, which undergo tremendous torque delivered by the gearbox geared down even further through a 2:1 reduction to the drive shaft. This situation resulted in a lengthy process of evaluating knurled rollers, smooth rollers, and polyure thane-coated rollers. In the end, the coated rollers delivered the response desired and handled the torque levels delivered by the motors.

An all-pushbutton-driven device requiring no software interface, the PowerNurse operates in three distinct modes: burrow, pad align, and transfer. During the burrow mode, belts are used to pull the patient onto the top of the device while belts on the bottom move the device under the patient. Done simultaneously, the result is the patient feels a much smoother transfer than with many other devices.

In pad align mode, only the top conveyor belts are energized. This aligns the patient and incontinence pad if necessary. Transfer mode energizes only the bottom belts, which transfers the PowerNurse, with the patient riding on top of the device, to an adjacent surface. Rotation and translation are available in any mode, and the result is a tank-like translation or rotation. Four Maxon motors are required to achieve all of the device’s operational modes.

This article was contributed by Maxon Precision Motors, Fall River, MA. For more information, visit 34459-321.

Motion Control Technology Magazine

This article first appeared in the October, 2011 issue of Motion Control Technology Magazine.

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