Motion Control Resources
Electromechanical Design Goes Green
by Kristin Lewotsky, Contributing Editor
Motion Control & Motor Association Posted 10/13/2010
Motion control advantages help OEMs design machines with high levels of overall equipment effectiveness, efficiency, and environmental friendliness.
At the time of the industrial revolution, even the most visionary engineer would have been hard-pressed to imagine the breadth of tasks that machines would eventually perform. From testing to assembly to packaging, machines today can take in raw materials at one end and turn out palletized product at the other. With every month that goes by, the operations, and the machines that perform them, become ever more complex and ever faster.
For a long time, the primary question was simply how to make motion control perform the task at hand. Today, with industry buffeted by economic and environmental forces, the question is not what motion control can do but whether motion control can do it cost-effectively and in an environmentally friendly fashion.
Overall equipment effectiveness (OEE), high-efficiency operation, green design -they’re separate concepts that are nonetheless interrelated, reinforcing one another so that executing on any one of the three more than likely means succeeding at the others. End-users who start out to buy a machine that provides low total cost of ownership (TCO), for example, discover that that same machine provides a reduced carbon footprint by virtue of its increased efficiency. For OEM machine builders, it adds to the sales story. For end-user it provides another way to enhance their corporate brand. “It's definitely all tied together,” says Jesse Henson, drives field sales manager at Baldor Electric Co. (Fort Smith, Arkansas). “Energy efficiency and green are becoming more important for industry.”
Overall equipment effectiveness is a metric that essentially expresses how closely the actual output of a machine approaches its theoretical output. Although the concept originated in manufacturing and can be used to analyze everything from the productivity of a shift to the manufacturability of a specific product, OEE also provides a useful way for thinking about machine design. Key underlying metrics for OEE include availability of production equipment, performance of that equipment compared to theoretical performance, and quality of product produced.
The push for OEE appears to be coming primarily from end users. OEM machine builders typically care about cost of components and ease of integration. It’s the end users who focus on operating cost. “They want to improve the overall productivity of their machines,” says Henson. “At the end of the day, that's what it's all about—getting more throughput and producing more product, which in turn pays for the machine faster.”
Indeed, OEE has become such a focus that it’s getting written into contracts. “It depends on the industry, but I do see end-users requiring OEMs to supply machines with a guarantee of a certain OEE level,” says Dan Throne, sales and marketing manager for the electric drives and controls division at Bosch Rexroth Corp. (Hoffman Estates, Illinois). “They have penalty clauses built into the contracts so that if a machine doesn’t deliver, the OEM takes a hit. It’s not fun, because some things are out of the OEM’s control, but it does push the technology, that’s for sure.”
It’s a challenge, but motion control can help. In the area of performance, motion control provides precision, robustness, and repeatability. It’s in the area of availability that the technology really shines, though. Electronic camming can increase availability by speeding changeover. Forget about spending hours or even days swapping out mechanical gearing. With electronic shafting, changing recipes can be as easy as toggling a command in the HMI.
Smart components fitted with onboard memory and processing power feature diagnostic functionality that simplifies troubleshooting and maintenance. Such devices allow systems to monitor attributes like motor torque, position, and acceleration, as well as the frequency of any oscillations or vibrations. Those parameters can give an enormous amount of information on system health. A difference in acceleration, for example, can indicate a change in load. A shift in vibration or temperature can reveal lubricant breakdown or unplanned motion caused by a loose coupling or ballscrew.
Today’s motion control systems can log these parameters in the controller. OEMs can set operating ranges for a machine before it leaves their floor and write software so that when any parameter goes out of range, plant maintenance receives notification. If a machine stops operating, the machine builder can pull off the entire fault history to find the cause, and do so remotely, if the system is networked. Device parameters can be stored on smart cards so that if a component fails, all the maintenance engineer needs to do is replace the failed device, plug in the smart card, and resume operations.
Smart diagnostics may be old news to motion control suppliers, but it’s not deployed as widely as one might expect, says Throne. “A lot of factories we go into are not the ones featured on the cover of a magazine as the most highly automated plant in the world,” he observes. “The vast majority of plants still have 30-year-old machines. Meanwhile, a lot of OEMs are under constraints to be competitive in the market, to get their machines installed quickly, and installation costs are typically paid for by end customers. I think as a result of all of those elements, a lot of end-users don’t utilize predictive maintenance as they could. It’s something I would love to see more of.”
Minimizing Failures, Maximizing Uptime
Smart components such as motors with integrated drives offer additional benefits beyond improved diagnostics. In a conventional, centralized architecture, the drives reside in the cabinet and connect to the motors via pairs of power and feedback cables. All those cables take time to connect, as well as costing money. Perhaps more important, cabling is the single biggest point of failure in machines. The more cables and connectors, the greater the possibility of downtime.
Integrated motor drives open the door to a distributed architecture. Instead of locating the drives in a cabinet, machine builders can place them out on the machine with the motors, daisy-chaining them together with a single line of cable. “Not only do we reduce cabling by 85%, which contributes directly to your reliability and your OEE, but we also reduce fabrication, assembly, and configuration time,” says Throne.
Safety options provided by motion-control systems likewise contribute to productivity. When a system jams, the basic protocol is to cut power, stop upstream and downstream operations, access restricted areas to clear the jam, then resume power, re-home, and bring up the line module by module. Newer safety components can allow operators to get the line back up and running faster. With safe motion, motors can function in Safe Torque Off mode, for example, in which the drive is disabled but maintains its position settings. Safe Speed mode goes one better: Not only do the drives remain powered up, but the motors can be used to help clear the jam, speeding the cleanup process. The result is a system that is back up and running far more quickly than before. “You’re able to open a guard gate in a safe operating mode, remove the jam, close the guard gate, and hit restart,” says Throne. “It just increases the efficiency of that line tenfold, when you add it up.”
Even before the year of $4/gallon gasoline, the U.S. Department of Energy had set minimum efficiency levels for motors. Given that the industrial sector uses about 30% of all energy in the United States, which is more than any other sector combined, efficiency requirements for motors - and machines - are likely to become more stringent.
Here, too, motion control can help.
Machines based on fixed-speed induction motors keep the motor rotating at a fixed RPM and use gearboxes, belts, and clutches to transmit speed and torque when required. Servo motors, on the other hand, draw power only when in use. “Motion control is an inherently greener technology,” says Tom Strigel, Kinetix Motion Control product marketing manager at Rockwell Automation (Milwaukee, Wisconsin). “Servo motion controls function individually, turning motors on and off as needed and at the level of power required, so there’s no wasted motion.”
“One of the big things we’re seeing now is AC motor customers going to servo style motors for AC-induction-motor-type applications has because of the energy savings,” Henson agrees.
Similarly, hydraulic systems must remain charged all the time. Unless a servo motor is energized to hold a specific position, it does not use any power when it is not moving. As a result, making the switch from hydraulic to electromechanical systems can pay big dividends. Throne points to MoCo Engineering and Fabricating Inc. (Spokane, Washington), which builds handling and stacking machines for the lumber industry. “They had done the stacker application hydraulically in the past but they struggled with the fact that with hydraulics, you always have to have the energy at peak because you work on a diaphragm and an accumulator-type system. They found they were able to save around 37% in their energy consumption when they went to electric drive systems.”
Efficient motors provide benefits above and beyond reduced power consumption. Drives not only draw a lot of power, they typically dissipate a significant percentage of it as heat that can hamper performance and lead to early failure. As a result, especially when packed together into a cabinet, drives require cooling that can range from fans to air conditioners. More components mean higher upfront costs, higher operating costs, and additional points of failure, which brings us back to OEE. The more efficient the motor, the smaller the amount of heat to dissipate.
Another tool for maximizing performance is regenerative power supplies. Regenerative power supplies regenerate the energy from decelerating motors back up the power lines to the utility grid. When you use a regenerative power supply and tie multiple servo amplifiers together with a common bus, you have an extremely energy efficient system, because while some motors are drawing power for acceleration, others are returning power from deceleration motors. “During braking, you’re basically capturing the power and putting it back into the system to be consumed by other parts of the system, so it’s not just wasted as heat,” says Strigel. The net effect is zero power draw from the grid.
All of the above features and techniques combine to make motion control a highly green option. Distributed architectures reduce the amount material used on a machine, whether it’s cabling or air conditioners for the enclosures. High-speed systems allow a single state-of-the art machine to replace several older designs, freeing up floor space and minimizing resource consumption. Above all, the technology offers performance and adaptability. “These mechatronic systems are more flexible so they’re able to run different packaging materials,” says Throne. “That means you can run more biodegradable materials on the machine if it’s more highly automated. There are just a million ways to go green.”
Component vendors are beginning to produce electronics with leadfree solder, , for example, in part with an eye toward satisfying regulations like the EU’s Restriction of the Use of Certain Hazardous Substances in Electrical and Electronic Equipment (RoHS). Originally aimed at consumer electronics, RoHS is broadening its mandate over time. “In the motion control business, we’ve been paying attention to it on a different level for the past six or seven years and have been working with suppliers to move toward a RoHS-compliant state,” says Strigel. “Having said that, until probably the last six to nine months, the RoHS directive really didn’t talk at all about products in our classification. It was much more oriented toward consumer products, but there is a RoHS II directive that starts to get into what comes next, now that the first wave has been implemented.”
When RoHS expands to cover industrial machines, the motion control industry will be ready. Whether it's a question of availability, performance, efficiency, or environmental friendliness, motion control provides a powerful means for machine builders and end users to achieve their greater goals. Technologies like hydraulics and fixed-speed motors might be able to get the job done; motion control gets it done well.
Thanks go to Michael Ballinger of Elopak for useful discussions.