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Micro annular gear pumps with DC microdrives for precision dosing

Micro annular gear pumps with DC microdrives for precision dosing Challenge
There is a wide range of applications requiring the targeted dosing of small volumes of liquid, and increasingly design efforts are being focused on developing ever smaller devices that are easier to transport, install or integrate into existing systems. For its new breed of compact, hermetically, sealed micro annular gear pumps for continuous dosing, German manufacturer HNP Mikrosysteme was looking to set a new benchmark for size and performance, with a pump that would be suitable for use with corrosive media, and would to be suitable for a large number of applications, including the more exotic.

The drive dimensions for the pump were critical, as was the performance. The drives had to be compact in size, and offer a high power density and a large speed range with excellent dynamics, enabling high-precision control of flow rates from the smallest volumes to a constant maximum throughput. The drives also had to match the gear pump's requirements for long service life and a seal-less design.

Solution
Typical areas of application for the pump are the transfer of crystallizing, air-sensitive or outgassing media, fuel cell technology, the delivery of urea solution (AdBlue) to remove NOx from diesel engine exhaust gas, or dialysis and analysis technologies.

To meet the application requirements, HNP Mikrosysteme worked with Faulhaber, the German motor manufacturer whose products are distributed in the UK by Aldermaston-based EMS. The solution came in the form of an electronically commutated DC microdrive with integrated speed controller. The brushless design enhances the service life and reliability of the drive. Motor-adapted variable speed control is guaranteed by a speed controller that has the same diameter as the motor and is mounted to the rear of the motor. This means that the user can easily adjust the speed via an analogue input with 0-10V. A digital input determines the direction of rotation. For additional monitoring functions, the digital frequency output provides a 15mA output signal with six pulses per revolution.

The drive supply voltage is 12 or 24V DC, while the 22mm motors achieve around 9W and feature a torque of up to 59.9Nm. Supply voltage to the speed controller is 5 to 28V DC via a separate flat ribbon cable. The motor efficiency of around 68%, combined with control electronics that offer greater than 95% efficiency, enables long operating times even in battery-backed mobile devices.

Results
The hermetically sealed pump head is driven by means of a powerful rare earth magnetic coupling, which prevents leaks from the drive end. Thanks to the annular gear design, the pumpable viscosity range is between 0.3 and 100mPas, with a pulsation of around 6% and a differential pressure range of 0 to 5 bar. The no-valve annular gear principle guarantees minimal shear forces during pumping. Use of the Faulhaber microdrive means that the pump measures only 22mm in diameter and 69mm in length, and weighs around just 100g. The pump is designed for 24V operating voltage and can transfer 4.8 to 72ml/min at up to 5 bar delivery pressure.

The rugged stainless steel enclosure and wide temperature range of -40°C to +85°C enable the device to also be used outdoors, for example for environmental measurements. The short-term overload capability of the microdrives supports such applications, as this allows increased pump breakaway torques, enabling the pump to cope with the higher fluid viscosities, for example, that can result from overnight temperature drops.
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