Machine Design
Energy efficiency as an economic stimulus

Energy efficiency as an economic stimulus

Given the current state of the global economy, one of the few reasons companies are investing in new equipment is to lower the cost of production, and energy efficiency is a big part of that, says Karl Tragl, executive vice president with Bosch Rexroth. “It’s one of the major drivers, both for economic and environmental reasons, that’s spurring future growth,” he says.

“We believe there are four principles surrounding energy efficiency. First, use the most-efficient components possible in new designs. Second, consume only as much energy as required. Third, when there is redundant energy, as in braking, recover and reuse it.” And fourth, in terms of engineering, use design and simulation tools to optimize size, processes, and cycle time.

These principles apply across all motion technologies. “On the electrical side, there are servos that let you recover power and feed it back to the grid, and optimize motion, speed, and acceleration,” says Tragl. One example he cites is the company’s new Fe frequency converters that offer on-demand control of pumps and fans. Another is the HRB regenerative-braking system that reduces fuel consumption and emissions in mobile equipment.

For industrial automation, there are variable-speed hydraulic pump drives that integrate frequency inverters or servodrives. “It’s a great solution because servomotors have efficiency greater than 95% and only use energy on demand, and they can recover what was previously wasted energy.”

On the pneumatics side, systems that produce high forces to actuate a cylinder but only minimal pressure to return to the start position use the least possible amount of energy.

And on the mechanical side, “modern linear-motion components and systems can increase energy efficiency of many different applications,” says Bernd Schunk, executive vice president for Rexroth’s Linear Motion and Assembly Technologies business.

“Friction is one of the most important factors determining the energy needed to drive an axis. Low-friction seals can significantly reduce drive-power requirements. Compared to standard seals, they reduce friction between the runner block and profiled rail up to 50%,” says Schunk.

It adds up to a big effect. About 10 million ball-runner blocks are manufactured around the world every year. Converting just half of them to low-friction seals would save up to 230 GW-hr of electricity per year for the Size 25 blocks alone, he says.

For another example of significant savings, says Tragl, look at large presses. “These are huge energy consumers,” he says. “By installing variable-speed pumps, plus other measures such as energy recovery — because you’re basically braking as the press drops down — we cut consumption from about 15,000 kW-hr/yr to about 5,000 in one instance.

“With regenerative braking on refuse vehicles, potential savings are around 25%,” he adds.

He notes that in the not too distant past, machines were designed primarily for automation or speed, not efficiency, so the potential for improvement abounds. “The return on investment is typically 2 to 3 years, then you’re earning money,” says Tragl.

Rexroth's new Fe Series frequency converters, with a power range from 0.75 to 110 kW, provide on-demand control of pump and fan drives.

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