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Coreless DC brush motor creates high power density and smooth torque control for medical pump

17 March 2021

An enteral feeding pump manufacturer has selected a coreless DC brush mini motor system to power and control its nutrition flow.

Combined with a gearhead and encoder, Portescap’s engineers integrated the customised package to provide high power density and smooth torque control. 

A European infusion system provider developing an enteral feeding pump required a compact motion solution. An enteral feeding pump, including its feeding tube, is used to provide nutrition to patients who are unable or unsafe to eat by mouth, as well as those with challenges swallowing or requiring additional nutritional supplements. This could include patients who have suffered from stroke, dementia, throat and mouth conditions, as well as patients who are not conscious. An enteral feeding pump is preferable to alternative intravenous (IV) feeding due to the former’s continued dependence on the stomach, meaning the avoidance of stomach muscle rehabilitation, especially for prolonged use, associated with IV.

An enteral feeding pump needs to be compact and lightweight to enable portability. However, the pump has to deliver sufficient torque to ensure continuous flow and this particular model needed to deliver liquids of both low and high viscosity. Feeding pumps require accurate and precise flow rate adjustment, dependent on the liquid type and patient requirement. A specific demand for this system required that the fluid had to be delivered in a smooth, continuous flow, avoiding peaks. The pump also had to generate flow across a wide range of speeds, serving patients requiring very low flow rates through to requirements for relatively high speeds. The medical equipment manufacturer engaged with Portescap based on its track record of solving precision medical pumping challenges, combined with its technical knowledge and ability to customise its motion solution to meet exacting specification needs. 

Portescap engineers recommended the Athlonix 22N brush DC motor with the F16 magnetic encoder and K24 gearhead, combined with the required mechanical customisation. With a continuous torque delivery up to 15.7 mNm from the 22mm motor diameter weighing just 53g, the motor achieves a high-power density. The small footprint is largely a result of the coreless design, removing the need for the rotor’s laminated iron core and replacing it with windings which create a self-supported design. The mini motor’s neodymium magnets also add to its performance and high-power density within a compact package. 

The coreless design also assists with smooth pump control, avoiding any peaks in the rate of flow. As the Athlonix motor doesn’t include iron laminations, torque ripple is very low, resulting in smooth pump delivery even at very low speeds. The ironless design also reduces the inertia and mass of the rotor which enables greater pump control precision. Accuracy of control was further enhanced with the addition of the Portescap F16 magnetic encoder. Providing position monitoring in a compact package, the encoder features Hall sensors for reliability over position and speed sensing. 

An additional benefit of the coreless design, the Athlonix motor operates with low noise and low vibration, factors which were important for bedside hospital use. 

For portability, the enteral feeding pump features battery power, meaning that energy efficiency is a key requirement. The Athlonix motor was recommended as it features precious metal commutation with low generated friction, providing operational motor efficiency up to 90%. Efficiency was further enhanced with the addition of the K24 spur gearhead to provide low current consumption at the require output torques.

The motion solution also provided the long lifetime required of 2,500-plus hours’ operation. The Athlonix motor’s precious metal commutation, well suited to mini motor low current requirements with continuous operation, is resilient to varying climatic conditions. The brushes are designed for long life use and the motor’s REE windings reduce electro erosion, improving overall system safety and reliability. Meanwhile, the magnetic function of the F16 encoder means that it is insensitive to challenge conditions, which could involve fluctuations in temperature, or ingress. 

The ability to work closely with Portescap’s engineers was also a key requirement for the pump manufacturer. Integration of the motor, encoder and gearhead was facilitated with close cooperation, including customised product development. Customisation options for the Athlonix motor includes coil modifications and custom shafts as well as a choice of sleeve or ball bearings. The F16 encoder has options including cable and terminal outputs, while customisation to the K24 gearhead includes custom shafts and application or condition-specific lubricants. As well as product customisation, Portescap’s engineers can also engage for mechanical integration.

Today, the enteral feeding pump is able to support the nourishment of patients, providing precision fluid control and reliability as a result of the advantages provided by Portescap’s motion solution integration. The cost-effective design also enables widespread production of the pumps to fulfil hospital and home requirements throughout Europe.

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