Motors: Taking control of materials handling; flexibility and energy efficiency
June 02, 2010 - MMH Editorial
When it comes to automated materials handling equipment, the two most important attributes touted by equipment manufacturers are flexibility and energy efficiency.
Those aren’t idle boasts. In fact, today’s conveyors, sortation systems, automated storage units and automatic guided vehicles are more flexible and efficient than ever. Making that possible are advancements in motors, drives, controls and the software that oversees and directs how an automated materials handling system operates.
You wouldn’t see those changes by looking under the hood at the power system driving a materials handling system, but the evolution is similar to that happening in materials handling automation in general: OEMs recognize that done right, the whole can be greater than the sum of its parts.
As a result, the motors, drives and controls industries are moving away from standalone products and moving towards the design of integrated solutions. That’s where the motors, drives and controls work together to deliver more impressive results than can be achieved in isolation.
“The over-riding trend is that we’re designing the mechanical system and the control system simultaneously,” says David Voynow, segment manager for material handling at Schneider Electric (847-397-2600, http://www.schneider-electric.us/). In the past, he adds, the bulk of the engineering time for a new system was done first by the mechanical engineers who designed the equipment that go into a solution. Once they were done, they tossed the project over the wall to electrical engineers to design the power system.
Since the bulk of the engineering time was devoted to the mechanical solution, the power systems were often an after thought. “Now, we want to design it all as part of the methodology rather than do it separately,” Voynow says.
That approach allows the systems to consolidate as many of the input/output, safety, power and control requirements as possible into a modular unit that is being located as close to the motor as possible. “If we do it correctly, we can reduce the complexity of how we produce these systems and we can create repeatable solutions that easily roll them out from one distribution center to the next,” Voynow says.
Here’s how motors, drives and controls are transforming automated materials handling systems.
Keep on motoring
Motors are the power behind the scene when it comes to automation. Today, end users are beginning to think about motors with an eye towards sustainability. “Motor-driven systems represent about 70% of the electrical load in an industrial facility,” says John Malinowski, senior product manager for AC motors at Baldor Electric (479-646-4711, http://www.baldor.com).
“As a result, some bigger companies are now looking at energy consumption and savings as part of the specifications for a new machine,” Malinowski adds. “They want to get motors that are sized right, drives where they need to have drives and they’re looking at environmental protections like stainless steel enclosures where it’s appropriate.”
For some end users, that may mean choosing high efficiency motors, which are 2% to 8% more efficient than traditional motors. But the drive for energy efficiency is also an example of how a systems approach to the design of a power system can deliver bigger savings than can be achieved with motors alone.
“Retrofitting a system with a premium motor is a great thing to do, but it’s an incremental increase in efficiency at best,” Malinowski says. “On the other hand, if I look at the whole system and swap out a worm reducer that’s 50% efficient with a helical reducer that’s 95% efficient, I only need a 5 horsepower motor to get the same output torque as a standard 10 hp motor. That’s a real savings.”
But the most efficient system is one where the motors are turned off, or only running when they’re needed and at speeds that are no faster than required to meet throughput requirements. “If I can put sensors that know when a box needs to move, then I can run the conveyor only when it needs to run,” Malinowski says.
Additionally, the cost of servo and linear motors has come down in price for operations like automated storage and retrieval and sortation that require precision movements. These motors are more precise and efficient than traditional motors, allowing an end user to get better throughputs at slower speeds. “When you’ve done all the conventional process improvements, this is the next step in improvement in your facility,” says Malinowski. “You can’t get these gains from the traditional movement of product through your plant.”
Getting the right motor is only the first step towards more efficient and flexible systems. “Using a more efficient motor has an impact,” says Ken Fry, a business segment manager for Rockwell Automation (414-359-9700, http://www.rockwellautomation.com/). “But, the way you control your equipment might have a bigger impact on what your energy bill might be.”
That’s where drives come into play. These are devices that take feedback from the motors and then analyze the data to more precisely control the motors. “All of the items in a control system are producing data,” says Fry. “The smarter OEMs are taking that data and turning it into information that allows the drives to truly run the motors smarter.” As a result, he adds, “drives are becoming a standard part of a conveyor offering.”
The most common of these is the variable frequency drive. This allows a conveyor or sortation device to vary the speed at which the equipment runs based on production needs. “Instead of running the motors at full speed for a full shift, as used to be the case, a variable frequency drives allows you to vary the speed of your conveyor system to meet your production needs,” says Fry. A variable frequency drive also brings the conveyor up to speed slowly, minimizing the power surge needed to get things moving.
A regenerative drive—a drive that’s used for tasks like directing the motion of a crane in an automated storage system—enables a user to return energy to the grid during certain tasks. “The classic way to handle the lowering motion on a system is to use a braking unit,” explains Alex Harvey, director of product management for AC and DC Drives, Control Techniques Americas, Emerson Industrial Automation (800-893-2321, http://www.emersonct.com). “But that just wastes energy because it dissipates.”
By using a regenerative drive with an AC motor, instead of a brake, the crane consumes power when it lifts a load for putaway, but creates power that is sent back into the grid when the crane is lowered. The result can be big savings. “We retrofitted an AS/RS system in New Jersey with regenerative drives and realized $10,000 in energy savings in the first year and reduced their maintenance costs,” says Harvey.
Finally, drives have gotten more compact and smarter, with computing power onboard. That allows them to be installed closer to the motor, where they can get more timely information on how the motors are running, and to replace a programmable logic controller, or PLC.
In this scenario, a signal from a sensor that material is coming down a conveyor can be sent directly to a drive, rather than going first to a PLC, which then routes instructions to the drives. Eliminating the intermediary step speeds up the response time of the system. Once the drive performs its job, it can communicate back to a supervisory PLC or directly to the next drive downstream.
And if one of those drives should fail, or need to go down for maintenance, another drive will notice and pick up the slack so that the system continues to operate. “What’s evolved is that we have really flexible architectures that allow us to balance cost, performance and redundancy,” says Harvey.
Getting under control
Software controls and PLCs are the final components in power and control systems. While PLCs and PC-based controls once represented two very different approaches to control, today they have morphed; PLCs are in essence powerful mini-computers that marry the reliability of a PLC with the open programming languages used by PC-based controls.
That has resulted in controlling devices that utilize commercial computer chips and computer languages like Windows CE. Some call these new devices programmable automation controllers, or PACs. They represent a big plus to users who want a more sophisticated control system without ripping out their legacy systems to install PC controls.
“In the past, you might have needed two PLCs for a job,” says Fry. “Now, with a PAC, you can control speed, motion and other process controls all in one device. Because it’s all in an integrated solution, the actionable information is much faster than it used to be.”
What’s also emerging, however, are control systems that use software to target an automation platform. Schneider Electric calls this “flexible machine control.” In essence, it’s a preconfigured process solution that can be easily rolled out and matched to a system. “With one piece of software, for instance, we can target a PLC, a motor drive and motion control to create a solution for gapping in a sortation system,” says Voynow. “The software can control the accumulation conveyor, a high speed merge and the sorter to precisely close the gap that is needed.”
The goal is to get closer and closer to controlling these systems directly by the motors and drives. “Think of having CPUs or smaller distributed PLCs at the motor with the logic built right in for that piece of equipment,” says Voynow.
These smarter systems are not only better at managing individual processes, they can also manage an overall facility for energy efficiency. “You’d be surprised at how many facilities are recharging their batteries at the same time they are running their conveyors, which means they’re paying peak energy rates,” says Voynow. “We can use these systems to manage a facility to meet production needs but to also maximize energy and sustainability.”
“In the last year, we have seen a large number of OEM customers targeting the retrofit market,” adds Rockwell’s Fry. “They’re keeping the steel and motors in place on their sorters and conveyors, and putting in new controls. People are going to their power and control systems to get more throughput in the system rather than replace something altogether.”