Motion Control & Drives


Maximising motor performance and energy efficiency

June 2023 Motion Control & Drives

The power usage of motors used in machinery totals 40 to 50% of the world’s electricity consumption, making these industry-essential devices a key energy reduction target. The market is seeing a proliferation of industrial motors claiming to offer improved energy efficiency. The latest inverter motors are also contributing to lower power consumption, as they adjust their rotational speed according to operating conditions. Furthermore, demand is ramping up for new-generation servo motors, which typically find use in industrial robots as they can rotate forwards and backwards for accurate positioning. These three motor types (high-efficiency, inverter and servo) all rely on one common component to help maximise performance and minimise energy consumption: bearings.

Worldwide endeavours to reduce power consumption have led to regulations requiring motor efficiency improvements. A motor’s energy loss comprises three factors: iron loss (heat generation from the iron core); copper loss (heat generation from the winding); and mechanical loss (due to bearing rotation, for instance). Although mechanical loss can be as small as 1% of motor power consumption, it accounts for 0,4 to 0,5% of global electricity use, which means the worldwide impact of any reduction is significant.

Low-torque bearings for high-efficiency motors

NSK evaluated mechanical loss from bearings using high efficiency motors.

In a two-pole high-efficiency motor running at 3000 rpm, the cause of 80% of mechanical loss was lubrication resistance. Optimising the grease quantity reduced mechanical loss by 60% in comparison with conventional bearings. The low-torque bearing developed by NSK uses special grease, increasing seizure life more than 2,7 times; and NSK’s specially developed plastic cage reduces mechanical loss to half that of steel cages because the plastic cage supresses grease agitation resistance between the cage and balls.

Ceramic-coated bearings for inverter motors

Inverter motors are useful for delivering energy savings in pumps and blowers. The trend is to increase the frequency requiring control (known as the carrier frequency) so that the motor can operate with a higher degree of accuracy. However, as the carrier frequency increases, electrolytic corrosion may occur due to high-frequency current in the bearing. Here sparks generate through the lubricating oil film between the raceway surface and rolling elements, causing local melting and unevenness. This effect also leads to abnormal running noise and seizure.

Some bearings for small motors feature ceramic balls that do not pass a current, to protect against electrolytic corrosion, but there are productivity issues with larger diameter ceramic balls required for medium and large inverter motors. To remediate this, NSK has developed an anti-electrolytic-corrosion, ceramic-coated bearing specifically for use in these inverter motors. The newly developed bearing exhibits excellent electrical insulation, with DC tests showing ten times more insulation than general ceramic-coated bearings. The NSK bearing demonstrates equivalent insulation with an AC power supply, satisfying an impedance of 100 Ω or more at 1 MHz frequency.

In terms of mechanical performance, the impact resistance of the coating is three times that of a general ceramic-coated bearing. Heat dissipation, which is a disadvantage of ceramic coatings, is suppressible using a relatively dense coating compared to that used on conventional bearings, extending both lubricant life and motor life. In tests, the temperature rise during bearing rotation was about 10°C lower than that exhibited by a general ceramic-coated bearing. The dense coating also means fewer voids and better durability.

Low particle emission bearings for servo motors

The precise positioning capability of a servo motor derives from transmitting or reflecting the LED’s light emission signal in the pattern engraved on the encoder plate, and feeding the received signal back to the motor controller. Contaminating the encoder plate’s surface with oil or other matter disables the signal reception and feedback of the position information to the motor controller, preventing regular operation.

In a servo motor for a robot, it is necessary to stop the arm and workpiece via an electromagnetic brake. Contaminating the brake plate with oil or other material causes brake slippage. Servo motors used in industrial robots and cobots must be highly reliable, so bearings should exhibit low particle emission to avoid contaminating the encoders or brakes. NSK has developed a bearing for servo motors that uses a low particle emission grease with optimised composition. The bearing provides excellent contamination protection.

The scattering of grease contamination decreases when using bearings with a non-contact seal and low emission. Furthermore, bearings with LGU grease and the light-contact DW seal show hardly any grease scattering – an effective countermeasure against encoder corrosion.




Share this article:
Share via emailShare via LinkedInPrint this page

Further reading:

Future-proofing SMEs with cobots
Omron Electronics Motion Control & Drives
Many countries around the world are likely to experience skill shortages over the coming decade, especially technical specialists. At the same time, product lifecycles are becoming shorter. Collaborative robots are easy to set up, and offer a quick and cost-effective solution.

Read more...
Flexible transport solutions for materials handling
Omron Electronics Motion Control & Drives
Omron has added a Selectable Autonomy functionality to the core software for its line of autonomous mobile robots

Read more...
Sun carries the load
Motion Control & Drives
When valuable lives are hoisted in the air, reliable load holding technology is at its utmost importance. That’s why you can count on Sun’s excellent load holding cartridge valves.

Read more...
Latest trends in pneumatics systems
Motion Control & Drives
Online teaser: There is a misconception that there is not much innovation in the pneumatics field, but a closer look reveals otherwise.

Read more...
Hägglunds Drives at Botswana exhibitions
Motion Control & Drives
Hägglunds Drives South Africa recently participated in the Botswana Mining and Technical Exhibitions.

Read more...
Agricultural chain solutions
SKF South Africa Motion Control & Drives
SKF agricultural roller chains and special combine, baler and drive chains are used extensively in the agricultural industry on a range of machines and equipment that includes combine harvesters and headers, planters, feed mixers, and balers.

Read more...
New smart, connected crane
Motion Control & Drives
Konecranes has launched its flagship Konecranes X-series industrial crane, the successor to its popular CXT model. It has a new compact design and safe, reliable technology that, thanks to its wireless upgrade capabilities, can adapt to customer needs now and in the future.

Read more...
Bosch Rexroth Africa strengthens its offering
Motion Control & Drives
Hydraulic and Automation Warehouse (HAW), a Bosch Rexroth Africa group company, has incorporated Power Team SA’s SPXFLOW and Bolting Systems into its offering.

Read more...
Lubrication system for Moroccan paper mill
SKF South Africa Motion Control & Drives
SKF enhanced personnel safety and increased machine reliability boosted uptime, and delivered substantial time and cost savings for a leading paper mill in Morocco with the installation of a complete Maxilube lubrication system on a paper machine.

Read more...
Revolutionising warehouse operations
Motion Control & Drives
With the warehouse industry requiring ever-greater efficiencies, Toyota Material Handling has introduced an articulated forklift truck that revolutionises warehouse operations, and promises heightened agility, unmatched precision, and elevated safety standards.

Read more...