Sustainable Motion: Benchmarking Energy Performance in Mechanical Components

Energy efficiency always has been and always will be part of mechanical engineering, but things have changed in that we’re now in an era of increasing restrictions and regulatory pressure to use less power.  

At the same time, however, engineers are being supported in making efficiency gains through new component versions and evolving best-practice approaches. 

Regulatory Pressure

While regulations governing energy efficiency in all mechanical systems become increasingly stringent, engineers need to pay special attention to asynchronous (induction) applications, explains Gena Hurst, product manager at Stober Drives.

“The synchronous world is very efficient, but in the asynchronous world, for example, conveying items of various weights and sizes, where you have to engineer for the heaviest the system has to handle, it’s much more challenging to minimize energy use,” she says. “Nevertheless, we’re now at IE3 for asynchronous applications and IE4 is coming.”

READ MORE: Actuators and Drives: Foundations of High-Performance Motion Systems

Based on the International Electrotechnical Commission (IEC) standard 60034-30, IE3 and IE4 represent progressive steps in energy efficiency, whereby IE3 signifies “premium efficiency” or the minimum standard for many asynchronized motors and IE4 denotes “super-premium efficiency,” offering better performance and reduced energy consumption.

Hurst asks us to imagine an asynchronous system where you want to move from IE3 to IE4, which is a challenge an engineer can approach several ways. One of these is to obviously decrease the size of system components where possible, Hurst says, and another is to use, or also use, components that run cooler and more efficiently.

“You could also keep the same component but there are costs to that,” she explains. “Looking at the motor for example, if you keep the same motor in going from IE3 to IE4, you may have to add more copper to it. This not only adds cost, but there is extra weight if the motor is conveyed, and that will take away some of the efficiency you gain with the extra copper. Look around for other solutions. There are many new innovations; for example, our permanent magnet motors that are already IE5.”

There are also advancements with traditional servo motors, explains Connor Robinson, Bosch Rexroth sales product manager. Some of today’s servo motors now have features like single cable connections, with feedback on torque, temperature and vibration used to achieve optimum performance and minimize energy use. “Rotors have also been redesigned on our traditional servo motors to achieve top efficiency by producing more power per unit of space,” Robinson says, “with low or high rotor inertia options to avoid inertia mismatch.”    

Nagesh Desai, senior engineering manager at Portescap, adds that in some devices (for example, battery-operated autonomous mobile robots), brushed DC motors often utilize precious metal commutation to minimize current consumption.

“Collector bars are typically made from silver alloys and brushes are composed of gold deposits,” he explains. “Electrically conductive grease, specially formulated to reduce friction and optimize brush pressure, is applied between the collector bars and brushes. This minimizes mechanical wear and also wear due to electrical arcing, helping maintain low current consumption throughout the motor’s lifespan.”

Another efficiency in brushed DC motor designs that also reduces costs is to use sleeve bearings made from sintered bronze, says Desai. These bearings are impregnated with specially formulated oil, which is retained in the porous structure created by the sintering process. The oil acts as a reservoir, continuously supplying lubrication between the bearing and shaft over the motor’s life, thereby reducing wear and maintaining low current consumption.

In addition, he says there’s also a current active exploration of using Soft Magnetic Composite materials to reduce core losses in motors to increase efficiency but notes that these materials face limitations in terms of mechanical strength and maintaining adequate density in thin-walled sections.

Motor Regulation

In the area of enhancing motor regulation and minimizing heat generation, several techniques are now being employed. “These include software-based simulation for electromagnetic circuit optimization, winding patterns designed for maximum copper fill and optimal magnetic field interaction,” says Desai, “as well as the use of high-energy magnets and iron-cobalt alloy laminations to reduce watt losses. Improving thermal management involves the use of external heat sinks with fins and integrated impeller fans.”

He adds that adhesive tapes made from highly thermally conductive materials further enhance heat dissipation.

READ MORE: Motion in Motion: A Reference Guide with Case Studies and What’s to Come

Another advancement to reduce power losses in a motor is to use drive electronics compatible with high-frequency pulse width modulation, says Ashish Kushwaha, a senior design engineer at Portescap. He also notes that wide bandgap materials such as SiC and GaN-based switching converters can also be employed.  

In addition, control electronics that support high sampling rates—such as high-end microcontrollers, processors and high-speed analog/digital devices—are utilized for precise torque and speed control.

To optimize performance, Kushwaha says new advanced control methods can be used, including Direct Torque Control (DTC), Field-Oriented Control (FOC) and adaptive control techniques. “More advanced approaches may also incorporate AI/ML-based algorithms,” he reports. “Also, advanced tuning techniques, such as frequency domain analysis, are applied to optimize loop tuning and enhance overall system performance.”

Efficiency Gains Through Coatings

Taking a look at efficiency advances with gearboxes, Desai reports that diamond-like carbon coatings are now applied to gear surfaces to significantly reduce wear and friction. This contributes to both lower current consumption and longer gearbox life.

He adds, “emerging trends in gearbox technology include the use of contactless magnetic gears. However, while they offer benefits such as reduced wear and maintenance, they are limited by the need for relatively larger sizes to transmit equivalent power, as well as higher costs and significantly lower operating speeds.”

Type of gearing also has a large impact on energy efficiency. Hurst notes that while there’s a wide range of gearing options for specific applications, Stober only uses helical cut gearing as it provides very high efficiency (95-97% transmission of torque from input to output). And because in this type of gearing, three teeth are in contact at any given time, torque transmission is spread out, gear chatter is avoided, and so on.  

“But you don’t want to just focus on a motor or gearbox,” says Hurst, “whether you swap in a more efficient one or tweak the existing one. Look at your entire system.”

Systems Approach

The best practice for gaining energy efficiencies, especially over the long-haul, is to look at the entire system.  

“Look at your cable, drive, your upstream situation, how much power are you losing when it enters your building and so on,” says Hurst. “If you’re running a motor at half its capacity or running a gearbox above or below its rated speed, you’re burning through more power than you have to. If your cables are too long, you’re going to have line drop. Look at your belts, pulleys, rack and pinion linear systems and ask yourself if you can reduce weight and size, which will reduce not just power requirements but wear on components.”  

READ MORE: How “Smart” Components are Getting Smarter: Valves, Bearings, Gearboxes and Brakes

Hurst has seen customers with heavy rack and pinion systems cut significant power use by removing tall parts of the axis and generally making it more compact and lighter. “You need to look at everything,” she says. “How hard is your current setup on the mechanics, and how can you be gentler, so to speak?

“Look at the motion profile in a fresh way,” Hurst adds. “There may be another solution for the motion that still meets the customers’ required cycle time but uses a lot less energy. Find the right solution that uses less energy, not just a solution to the motion requirements.”  

Recaptured Energy

Part of your system-level analysis to increase efficiency should include how to integrate technologies that enable electricity reuse.

“A lot of our customers are looking at shared power in DC bus sharing systems that tie together two axes,” says Hurst. “The axis that is regularly doing a fast deceleration acts as a generator. The bus system takes that power back to the driver via a copper drive or wiring, and it’s used for the axis that’s speeding up, say, for a pick and place application. You’re using power you’ve already paid for much more effectively.”

Similarly, Robinson explains that when a drive servo motor is decelerated or brought to a sudden stop via a brake resistor, its kinetic energy is lost to heat. “Our technology takes that energy and charges a common DC bus to be used on accelerating motors,” he says. “The power supply module generates a DC bus voltage from the mains voltage and delivers it to motor-integrated servo-drives.” The DC bus voltage is therefore kept at a constant level. In addition, firms like Bosch have drives with “energy buffering,” meaning energy is stored in capacitor banks, battery packs or kinetic motors.