Energy Efficiency: The Secret to Sustainable Machines

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The focus for machine design is no longer simply maintaining acceptable production rates at an appropriate level of quality. Automation professionals are now deploying technologies in clever ways to improve the energy efficiency of their automated machinery.

Because their company invests in both, this group of machine designers was able to specify smaller motors and recover otherwise wasted energy on the new high-speed beverage palletizing machine that they had developed recently. Because of these and other efficiencies, the new machine now has a cycle time that is 15 percent to 20 percent faster than its predecessors, and consumes about 20 percent less energy.

These engineers have discovered what a growing number of their colleagues in other companies are finding: automation vendors have not only developed energy-efficient technology, but have also acquired substantial expertise in deploying it. Both this technology and expertise can be quite helpful to machine designers in mitigating rising energy costs and in adhering to tighter governmental environmental regulations.

In T-Tek’s case, the designers worked with the engineering staff at Bosch Rexroth Corp., in Hoffman Estates, Ill., to install one of that vendor’s servo systems. Scott Hibbard, vice president of technology at Bosch, attributes the success to four sustainability principles that his company applies to help users reduce the environmental impact of their machines: efficient components, energy recovery, energy on demand, and energy-conscious design.

Application of the first principle, building motion-and-control systems from efficient components, allows engineers to reduce the need for energy just about everywhere in a machine. Hibbard offers the examples of reducing sliding friction with roller bearings and adjusting power consumption on subsystems with intelligent drives wherever possible. Another example is reducing energy losses by installing pulse-width modulation (PWM)-driven, permanent magnet motors with segmented windings. “PWM has a much higher efficiency, less heating in the motor, and low losses in the bank of power transistors,” says Hibbard.

In automated machinery, motors are probably the most important component to consider for sustainability. The reason is that, according to most estimates, they account for at least 60 percent of industrial consumption of electricity.

Furthermore, “according to the U.S. Department of Energy, switching to a motor with a 4 percent to 6 percent higher efficiency rating can pay for itself in just two years, if the motor is in operation for more than 4,000 hours a year,” adds Brian MacCleery, product manager for the industrial embedded segment at National Instruments Corp., the Austin, Texas-based test and automation supplier. For this reason, many experts among users and vendors alike advocate using premium efficiency motors to reduce costs, as well as energy consumption and greenhouse gas emissions.

Improved Motor Efficiency

A characteristic of these premium motors is that they tend to be smaller and more compact. Boosting the efficiency of ever-smaller motors is a challenge that requires constant innovation in rotor, winding, stator and housing designs. “A bigger motor usually has a better efficiency than a small motor with the same power,” explains Harald Poesch, product marketing manager for servo motors at Siemens Industry Inc., in Alpharetta, Ga.

Another factor to consider is that every motor has a different efficiency at different speed and torque. “Efficiencies generally track at over 90 percent for a servo motor in the optimum range, and below 30 percent efficiency at very low speed,” adds Poesch. For this reason, vendors such as Siemens have been not only concentrating on maximizing efficiency at specific speeds, but also offering motors with high efficiencies over a wide range of speeds and torques. To avoid gearboxes and the energy losses associated with them, they also have been designing direct drive motors for low-speed, high-torque applications.

Of particular importance to T-Tek was Bosch Rexroth’s second sustainability principle of energy recovery. Also known as power-source regeneration, the principle exploits the fact that motors can act as generators whenever they decelerate, returning some energy to the power system, rather than dissipating all of it as heat. Using this technique, machinery can emulate electric cars that recharge their batteries as they go downhill or come to a stop.

“This has long been used in the kinds of drives found on metal-cutting machine tools—especially those with large or high-speed spindles—because of the great amount of energy that can be returned,” reports Hibbard. “In other areas, such as automation and packaging, this practice has not been as widespread.”

His third sustainability principle, energy on demand, is to generate only the amount of energy needed. For many applications, this means installing variable-speed drives so that motors fitted to them can run at slower speeds when running continuously at full speed is unnecessary. The drives also eliminate less efficient mechanical means for varying speed, and can reduce power-line disturbances and power demand at start. The energy savings with the correct drive-motor combination can often exceed 60 percent, according to Mark Kenyon, product manager for AC drives at vendor ABB Inc., in Milwaukee.

The classic example is a conventional hydraulic pump, which often relies on an induction motor that runs continuously and requires air conditioning or another system to dissipate heat. “The first step to improve efficiency is to control the induction motor with a variable-speed drive to bring the pump into an idle mode when possible,” says Hibbard at Bosch Rexroth. “This process greatly improves efficiency.”

He notes, however, that a variable-frequency drive on an induction motor may not be responsive enough when an instantaneous hydraulic response is expected. For these applications, he suggests replacing the drive and motor with an intelligent servo drive and permanent-magnet motor. “Intelligent drives can actually be part of the cycle process, monitoring the energy need and adjusting pump output accordingly,” he says.

Driving Efficiency

Until recently, the energy savings from using drives was often transparent to users because it had to be calculated using theoretical software tools. “Today’s drives have the ability to display the actual energy savings in currency,” says Kenyon at ABB. “In addition to real-time energy savings, today’s products can also display the greenhouse gas reduction by showing how much CO2 (carbon dioxide) has not been emitted.”

Drives can contribute to sustainability in other ways. They, for example, offer better control over operating parameters—current, acceleration and torque. Better control over the motor, in turn, helps to improve productivity by making quality control easier, decreasing scrap rates, and reducing maintenance problems from wear and tear.

Kenyon adds that another important contribution to sustainability is reducing the hazardous materials being put into landfills. “To that end, today’s drives comply with the Reduction of Hazardous Substances guidelines, which eliminate the use of lead, hexavalant chromium and cadmium,” he says.

When applying the fourth sustainability principle, energy-conscious system design, engineers look at optimizing the machine as a whole, not just one component or a group of subcomponents. Increasing the efficiency of the machine usually reduces energy consumption per piece. An oft-overlooked means of increasing efficiency is to shorten the cycle time. “Using 20 percent more energy to reduce a cycle time by 40 percent is a net savings,” notes Hibbard.

An optimization project should also include an analysis of how the machine consumes power. The first step is to identify how it is consuming and wasting energy and other resources. “You can’t control what you can’t measure,” explains Doug Burns, manager of sustainability practices at Milwaukee-based supplier Rockwell Automation Inc. For this reason, he recommends reviewing machines for fitting them with appropriate sensors.

Adding Sensors

The kind of sensor depends on the machine. “In many cases, it may be as simple as adding a power meter on the main incoming feed,” he says. “Putting a $750 to $1,000 meter onto a high-end converting machine is not a big issue. If, however, it’s a $40,000 semi-automatic machine, then you’re not going to put a $750 meter on it.” In that case, an intelligent overload relay or something else in the existing control system may be able to provide an estimate of energy consumption.

The next step of a power-consumption analysis is to study the trends in the data, looking for opportunities for generating efficiencies in the system. One tactic is to focus on the largest points of energy consumption in the duty cycle, specifying or installing whatever energy-efficient components would be practical for reducing that consumption. Because motors are the components that usually consume the most energy on machines, many engineers begin with high-efficiency motors.

Because a high-efficiency motor may save only 2 or 3 efficiency points, Burns recommends looking at the mechatronics of the entire power train—gearboxes, gear reducers and mechanical drive trains, as well as the motors. Those other devices may be operating in the 50 percent efficiency range. “Can you do this with higher-efficiency gearboxes, direct-drive motors or lower-power drives?” he asks.

Another tactic for analyzing trends is to find wasted motion. “We’ve all been by a piece of equipment running without cans on the conveyor, if you will,” offers Burns. His solution is to reprogram all of the equipment to run at current production rates. If nothing is going through a machine, then the controller should turn off or phase down the conveyor and other energy consumers—keeping in mind, of course, the need to power up quickly. Sometimes, the sequence or profile of a power-up can affect power consumption.

A multidisciplinary team of controls and mechanical engineers should conduct such analyses. A number of multidomain simulation tools, such as NI SoftMotion for SolidWorks, exist for streamlining the effort. These tools simulate mechanical motion and control software together, which allows multidisciplinary teams to optimize machine designs. “I can make the mechanicals lighter,” says MacCleery at National Instruments. “I can choose the right size motor. And I can even design my control software before the actual machine is built.”

Schneider Electric, in Raleigh, N.C., also recently introduced a multi-domain solution called MachineStruxure architecture for optimizing machine designs. Part of the vendor’s EcoStruxure energy-management architecture, the software allows designing, commissioning and maintaining logic, drive, motion, and human-machine interface (HMI) controllers in one environment. The company claims that the embedded intelligence can help users to generate energy savings as great as 30 percent.

Bottom line

To illustrate the benefits of a system-wide analysis, Poesch at Siemens offers a pump application in which a conventional motor is connected directly to the power supply without a drive. In this scheme, the motor runs at only one speed when it is on; the only other option is off. “By switching to a high-efficiency standard motor, the machine designer or retrofitter could raise the efficiency a few percent and therefore save some energy without sacrificing any performance,” he says.

Greater savings would often possible by adding a variable-speed drive and synchronizing it with pressure, flow or another appropriate control parameter to allow adjusting the speed of the motor to the requirements of the system. The next level of analysis would entail determining profiles of the dynamics and speed of the motor throughout the machine’s operating cycle. Armed with this information, you can select the optimal motor and drive for the machine.

Taking the trouble to conduct such a thorough systems analysis, rather than simply retrofitting with the latest high-efficiency motor, can pay handsome dividends. “It would be quite feasible to realize energy savings in a range from 2 percent up to 70 percent, depending on the application,” says Poesch.

For most applications, however, Burns at Rockwell reports more modest returns. His rule of thumb for savings is 20 percent to 25 percent for machines such as packaging and conversion machines that have undergone technology upgrades and programming optimization. With returns such as these, it’s no wonder that the secret has gotten out that sustainable machines can pay.