Motion Control Resources
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New Motion Options Boost Productivity and Savings
by Kristin Lewotsky, MCA Contributing Editor
Motion Control & Motor Association Posted 08/14/2014
Safety, onboard memory and intelligence bring end users rapid return on investment
With the rising cost of resources and energy, end-users are under pressure to do more with less. Gone are the days of building a machine to churn out a single product for a decade. They need the flexibility need to be able to change production on a daily or even hourly basis. They need to minimize power consumption, downtime, and staff. Above all, they need to minimize cost. Today’s motion control offerings provide a way to do all of the above.
“The technology has changed in the motors, the control technology, the drive technology, and also in the network technology, says Chris Brogli, Global Business Development Manager for Safety, at Rockwell Automation (Lexington, Kentucky). He brings the perspective of almost three decades as an automation owner, then integrator, then supplier. “Motion control systems are becoming more and more integrated and smarter and smarter, with features that allow us to enhance things like efficiency, throughput, and overall equipment effectiveness,” he says, “and all of this is happening because of the changes in the technology.”
The classic value proposition of electromechanical shafting has always been the ability to make changeovers by selecting a new recipe in the HMI in minutes instead of spending hours or days changing out gears and tooling. Today’s components have taken that to a new level. It’s not a question of just faster changeovers; sometimes, the changeovers are done on the fly. In automobile manufacturing, for example, automatic vehicle identification systems allow the line to determine the vehicle being manufactured and identify immediately what needs to be done.
This level of responsiveness is also useful in packaging applications requiring greater flexibility. Instead of filling a pallet with identically sized boxes, one pallet might involve 10 different carton sizes in a complicated packing layout. The system needs to be smart enough to adjust to that and build the pallet layer appropriately.
Adding intelligence can increase productivity in other ways. Consider a machine that requires 30 minutes to come up to speed. Turning it off when the workers leave for their one hour lunch break means losing 30 minutes of production time when they return. The alternative is to squander power running the machine in idle mode when it is not generating product. With intelligence, the machine can shut down at the start of lunch and then restart 30 minutes later so that by the time staff returns, equipment is ready for operation, maximizing throughput.
Today’s machines also benefit from increased speed, both from faster processors in the drives and controllers and from the benefits of ethernet-based network protocols. “Internal processing speed is a key component of a motion drive and system that the customers use because people want more output for less cost,” says Michael Mikolajczak, Product Line Manager at ABB (New Berlin, Wisconsin). “In the millisecond response world, protocols like EtherCAT and the corresponding devices can provide the extra output.”
Network-based communications also enables more sophisticated safety applications applied zone wise in order to minimize worker in capital equipment arm while maximizing output.
Energy harvesting over a shared power bus is an increasingly common technique. After all, anybody driving a hybrid vehicle knows about regenerative braking. The technique provides more than just power savings, however. Traditionally, in a conventional machine with multiple motors, you would need to size the drive front-end to accommodate the “worst case” motor loading scenario when, in reality, that worst case may never occur. More often than not, this means wasted energy. Applying regenerative technology using a common DC bus configuration, however, allows machine builders to significantly downsize the drive front-end and reduce the overall energy consumption of the machine. “We’ve had a converting application where we use a common DC bus configuration,” says Ken Kerns, Marketing Manager for the Motion Control and Low Voltage Drives Business with Siemens Industry (Norcross, Georgia). “The total output was around 500 A and it used conventional dynamic braking methods to control motor speed. With a common DC bus configuration, we were able to down-size the front end to 170 A and completely eliminate the braking module and resistors. We also used a smaller cabinet with less cooling, so it was even more efficient.”
The new generation of drives leverages onboard intelligence and memory to modify performance in real-time. Rather than simply trying to harvest energy during decelerations, these components are designed to dynamically adjust power consumption under a changing load, courtesy of sophisticated algorithms. This goes beyond harvesting a fraction of the energy spent – it involves spending less energy to begin with and can significantly reduce cost of ownership over time.
It also increases motor lifetime. Technologies such as flux monitoring allow the drive to evaluate the effect of load and reduce motor flux to minimize motor temperature. This increases motor lifetime and decreases unplanned downtime, enhancing overall productivity.
Running a motor at full speed either unloaded or partially loaded also wastes energy. “If you have a system with any kind of duty cycle on it, then variable speed drives can help,” says Kerns. “You don’t want to just run it at 100% speed and use mechanical means to control the output. You need to be able to provide the control to that motor that the output requires.”
Drives can also be adjusted to minimize peak power consumption (see figure 1). In conventional systems, drives initialize at top speed, generating a power spike every time they’re turned on. This can be a problem because in many cases, power companies set pricing for the quarter based on peak consumption. State-of-the-art drives can be set to ramp up slowly. The ability to minimize peak consumption or more effectively normalize it can provide big savings over time.
“While it’s nice to have regenerative braking, if we can somehow control peak demand, that’s where the big savings are,” says Arnie Mueller, Director of Operations at Bosch Rexroth (Hoffman Estates, Illinois). Consider a three-axis punch press. At a given point in time, two axes may be accelerating while another is decelerating. If the drive system can store that burst of energy from the decelerating axis access without putting it back on to the AC mains shared bus, it can be available for use by another drive. The system can exceed the standard bus voltage a certain amount before absorbing the regenerated energy back into the AC mains.
“What’s critical about that is if you have enough machines that can limit the peak power draw, then you don’t have to end up paying a higher energy rate,” he says. “The important thing to note is that this has to be designed in from the beginning, when you’re laying out the machine, though. It’s not something where you can come back after the fact and turn on.”
Today’s drives and design tools can also assist with power factor correction. Power factor can be thought of as the ratio of the actual Many utility companies will penalize industrial customers who do not operate at a certain power factor.
Part of the productivity trend involves maximizing uptime – after all, if your system is undergoing maintenance, it’s not manufacturing product. At the same time, to minimize the equipment failure, machines require regular care like lubrication and tuning. Other tasks like cleaning may not be simply advisable but mandated by law, for example in the food processing and pharmaceutical industries. Too often, the question becomes not whether but how much production time will be lost to the greater goal. Even proactive companies who schedule downtime quarterly or monthly may not have sufficient hours or staff to address all the activities that need to take place.
That situation is changing, however, thanks to enhanced safety functionality in machine design. "10 years ago, you designed the system to operate and then you figured out how to work around it,” says Brogli. “Now, handling activities like cleaning and servicing and minor adjustments can be addressed while you’re designing the system.”
Some of the newer safety capabilities play an important role. An operator cleaning intake rollers on a printing machine, for example, would normally have to clean the accessible surface, step out of the enclosure to jog the machine, stop the machine, reenter the enclosure, clean, and repeat. With Safe Direction and Safe Speed, as applied by safety controllers or safety-enabled drives, a machine builder can include a cleaning mode that moves the rollers the opposite direction at a safe speed. This would allow the operators clean the rollers continuously.
Brogli cites a food and beverage company that spent hours each shift cleaning a machine using the old-style clean-and-jog process. By applying Safe Speed and Safe Direction, along with a Safe-Position protocol that allowed limited safe operations when the enclosure was breached, the company was able to cut cleaning time from six hours to less than two hours. “They were able to gain an extra half shift of production,” says Brogli. “Instead of manufacturing product 16 hours a day, they were doing 20 hours a day.”
Gary Thrall, Senior Product Support Engineer at Bosch Rexroth, points to a manufacturer of electronic fuel injectors that reduced cycle time by 10% using Safe Direction. Under the previous process, the operator had to reach through a light curtain to adjust a part before the machine slowly pulled away, governed by Safe Limited Speed. All risks that would result from higher speed involved motion of the machine toward the operator. Adding Safe Direction ensured that the machine under no circumstances could move the operator's hands into moving parts. As a result, the manufacturer was able to move the parts away at top speed immediately after the operator performed his or her task, increasing throughput while keeping the worker safe.
The reduction in cycle time opens up multiple productivity options for an end-user. “If they want to increase production, they can do it without capital expense,” says Thrall. “If they want to maintain production, they can reduce the number of operators and save money there. They can also do preventive maintenance on the machine during the 10% of time saved. You have three different ways to save just by cutting cycle time by 10%.”
Cost of ownership--the big picture view
We all know the drill for capital-equipment purchases – put out a request for proposals, evaluate the results, and make a decision. Unfortunately, all too often that decision is driven primarily by the capital outlay. It’s an understandable dynamic, although not particularly helpful. At many end-users, the manager responsible for the output of the manufacturing line may justify getting a new machine but the purchasing department handles the acquisition. Often, that capital equipment budget is decoupled from the operations budget that pays for power, maintenance, etc. The priorities of one are not the priorities of another, especially since the results are so broadly separated in time. Meanwhile, the machine builder knows that to win the job, they need to come in with a low bid. The result is that the key stakeholders have conflicting objectives and end-user companies wind up paying far more than necessary over the lifetime of the machine.
The Wall Street carrot-and-stick routine of quarterly financials notwithstanding, companies compete over the long haul, not on the basis of a single purchase. Manufacturers need to take the big picture view of total cost of ownership (TCO) versus just total cost of acquisition (TCA). The kinds of capabilities we’ve been discussing all contribute to dramatically lower TCO. Given that the average lifetime of the electronics on a machine between retrofits runs about 10 years, those savings can add up. “From a motion control standpoint, the purchase price is 5 to10% of the TCO while the rest of it comes from the energy uses and the lifetime operation of that machine,” says Jim Grosskreuz, Product Manager, Rockwell Automation (Meqon, Wisconsin). ”Your upfront cost may be more, but your total cost of ownership is going to be much less due to tens of thousands of dollars in energy savings over the long life cycle of that motor.”
Expect this to be an ongoing trend in coming years as rising energy costs force organizations to take a holistic view. “That’s something that we’re consistently hearing from the high volume manufacturing companies: smarter, faster, and more power efficient,” says Brogli. “They’re putting things like power consumption, energy consumption, uptime, scrap break, reducing number of injuries, and so on into their machinery specifications. I think taking a holistic approach to machine design and implementation is what’s making the top companies the best. It’s a much different approach than when I was in manufacturing and working for end user 20 years ago. That was not even a thought.”
The shift is underway and factory automation industry needs to prepare for it. “Once the end users understand the benefits, they’re going to push for that technology,” says Mueller. “OEMs need to have these types of options ready to go.”