Page 12 - Industrial Technology EXTRA 24th May 2021

requirements of the application are then considered. applications such as medical therapy systems. The
Operational lifespan can be a key consideration increased life does carry a higher cost, however.
for the application. Medical products such as
oxygen concentrators and anaesthesia machines Power consumption
require the pump to last many hours of operation For applications that will be battery driven, power
without degradation in performance, which impacts consumption is an important consideration, and the
on the choice of motor. Unlike electronically efficiency of the motor is key. Slotless or coreless
commutated motors, iron core and coreless motors designs provide the most efficiency, with their
utilise brushes for communication, which wear over unique coil design minimising mechanical losses.
time due to friction and arcing. Motor life is dictated Slotted designs, seen in stepper and iron core
by the material of the brushes used. Options are motors, are the least efficient as the high iron
available to extend the brush life, including precious content produces significant electrical losses.
metal materials. In general, with their layered coil Another advantage of the slotless coil design, as
design, coreless motors will last up to four times well as from coreless motors, is reduced weight,
longer than iron core motors. However, where long and this can be a key consideration for portable
life must be assured, design engineers are best equipment such as gas analysers.
served by brushless DC and stepper motors. With the motor selection impacted by so many
Looking beyond commutation, the key point of different parameters, choosing the optimum product
wear common to all motors is the bearings. Two can be a challenge, and often tradeoffs must be
main types of bearing are available – sleeve and made to satisfy the specific requirements. But
ball. Sleeve bearings have lower force and life armed with the knowledge the advantages and
ratings (approximately 3,000 hours), but at a lower disadvantages of the various technologies, the
cost. Ball bearings offer significantly longer life design engineer can be confident of finding a motor
(approximately 20,000 hours) and withstand higher that meets both the performance requirements and
radial and axial loads (typically twice as high as price sensitivities of the application.
sleeve bearings), making them ideal for demanding www.portescap.com

May 2021 • INDUSTRIAL TECHNOLOGY EXTRA • p12