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DRIVES, CONTROLS & MOTORS


WHY SPECIFY A ‘MICROMOTOR’?


Micromotors are being specified for applications ranging from rehabilitation exoskeletons to the Rovers used to explore planets, and even for use in agritech robotics. But what are their benefits and why should a designer consider specifying one? Rachael Morling finds out from EMS


B


eing smaller in size and lighter in weight than conventional motors, micromotors offer benefits for a huge range of


applications, including in the medical sector as well as in agriculture and even in space. They are optimal for applications where accuracy is essential, as they offer precise speed control and are simple to control due to their linear performance characteristics. As an example, the main difference between


a FAULHABER DC micromotor and a conventional DC motor is the rotor, which consists of a self-supporting skew-wound copper winding instead of an iron core. The lightweight design of the rotor results in rotation without cogging, as well as a low moment of inertia, producing a highly dynamic performance. When looking for a motor, designers


must specify the power and size constraints of their application. If it is a motor for a motorised prosthetic, for example, it will need to be


super light so it doesn’t fatigue the user. In applications that require


extremely efficient micromotors, designers should specify a precious metal commutation system due to its low contact resistance. In contrast, micromotors with graphite commutation systems are ideal for higher power applications, while still maintaining long operational lifetimes. Thanks to their small size,


micromotors are frequently used in medical equipment where they help to prevent the equipment from becoming too bulky. As an example, when used in prosthetics, they allow for agile, precise movements, such as the flex of a finger to manipulate a small object. Micromotors are also ideal for providing


Micromotors are used in motorised prosthetics


high torque to power the patient’s movements, but must be lightweight, so micromotors are frequently chosen for this application.


MEDICAL DEVELOPMENTS Micromotors are, in fact, helping to advance rehabilitation equipment. Mobility aids such as wheelchairs, lifts and prosthetics, provide patients with support and assistance. In order to attain the force needed to physically support a patient, many of these mobility aids are driven by powerful, high precision micromotors. In particular, powered prosthetics and exoskeletons are at the forefront of rehabilitation engineering. There are over 45,000 people in England who are benefiting from lower limb prosthetics alone. However, if the prosthetic is


robotic, it must be lightweight to reduce


strain for the user and to provide greater


comfort. The powering motors therefore need to be small in size to


avoid making the prosthetic bulky. This allows the


prosthetic to perform agile movements and look closer


to the typical human form, while helping with activities such as reaching for an item in a kitchen cupboard. The motorised prosthetic


high power to medical equipment while ensuring smaller size. Exoskeletons, for example, are a piece of medical technology that provide mobility and independence to injured or disabled patients. They require a


must perform with precision and variable functionality – it must be able to forcefully pull open a door or hold an egg securely without cracking it. The motors must therefore be highly accurate to ensure the prosthetic executes its actions correctly, such as pressing a lift button on target. In addition, for patients who have lost mobility in their limbs due to a spinal cord injury,


Motors are a crucial element of rehabilitation exoskeletons, being responsible for driving the patient’s movements and supporting their gait


rehabilitation exoskeletons can be a revolutionary part of their recovery process. Rehabilitation exoskeletons offer an alternative way to get the patient moving, and offer greater independence, mobility and quality of life benefits than using a wheelchair alone. Motors are a crucial element of these


rehabilitation exoskeletons, being responsible for driving the patient’s movements and supporting their gait. The motor systems must be precise in order to replicate human movement, and offer the optimal amount of torque and motion control. Available from EMS, the FAULHABER BXT series motor is ideal for rehabilitation equipment as it has a flat construction, which helps keep prosthetics and exoskeletons streamlined in design. Thanks to its innovative winding technology, the series can deliver torque up to 134 millinewton metres (mNM), aiding powerful movements. EMS also supplies complementary encoders to the series, which ensure precise speed control of the motors.


APPLICATIONS So, outside of the medical sector, what other applications are micromotors suitable for? Micromotors are used on space Rovers to


power camera movement and the collection of rock samples. They are ideal here because they can deliver high power from a small assembly, preventing the Rover from becoming too bulky to transport to space. Micromotors are also ideal for agritech robotic


applications. Tiny motors allow miniature robots to manoeuvre delicately between rows of crops to remove and kill weeds without causing soil damage and compaction. The high power to weight ratio of the motors helps keep the total weight of the robot light while ensuring the motors are powerful enough to endure the process of weeding a large area of field without needing regular maintenance. FAULHABER micromotors are made in a finely


controlled manufacturing process that ensures they perform with reliability and repeatability, allowing precise control of movements.


EMS www.ems-limited.co.uk


MARCH 2022 DESIGN SOLUTIONS 21


FEATURE


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