What's New in Motion Control Applications?
| By: Kristin Lewotsky, Contributing Editor
It’s easy to think of engineering as finding a solution to a problem but that is not always the case. Sometimes, improved solutions prompt users to apply them to new problems or to apply them in different ways to existing applications. That’s certainly the case for motion control right now. The technology sector is in flux like never before. From industrial networking and smart factories to auto-tuning drives, smart conveyors, and kit motors, the technology is designed around performance, flexibility, and ease of use.
“It’s a cool time to work in automation because the technology is so amazing these days,” says Scott Carlberg, product marketing manager, Yaskawa America (Waukegan, Illinois). “For end-users and OEMs, it’s easier than ever to improve efficiency and throughput. They don’t have to spend a couple of days fine-tuning their whole machine.”
Make it easy
From OEMs to end-users, engineering staffs have become less deep across the board. The staff that remains needs to focus on the core value proposition — analytical instrumentation for medical testing, semiconductor fabrication, etc. In the case of heavy industry like mining, marine, and wood processing, they may not have had the staffing to deal with electromechanical systems to begin with. In response to broad demand for ease-of-use coupled with performance, vendors up and down the food chain have begun focusing on offerings that serve these needs.
Auto-tuning is one example. Tuning a drive with the standard PID loop techniques can take hours, or even days of work by skilled engineers. The first auto-tuning drives could get performance to a first approximation, but somebody still had to get out a screwdriver and fiddle with the potentiometers to make the system work right. The latest versions, however, offer a high degree of sophistication. Sure, the most demanding of applications might still require some work by an engineer with experience but for the most part, auto-tuning drives work as advertised. The best of them continuously adjust to changes in machine condition and send an alert over the network to warn of impending problems before they lead to failure.
The broad availability of components compatible with industrial networking takes ease-of-use one step farther. Plug into any port and you can access the entire system. If the machine is connected to the Internet, OEMs and integrators can easily monitor performance and troubleshoot errors. They spend less time on airplanes flying to far-flung factories and asset owners spend less time pacing next to a line that’s gone down and watching the losses mount. Instead, they can let their line run and harvest information to better understand operations. If a component fails, they discover the reason more quickly and get things rolling again sooner.
In a world of software-defined radio and software-defined networking, we’re moving rapidly toward software-defined automation. Changeovers take minutes instead of hours or days. Network machines with web-server functionality can be viewed remotely from devices ranging from laptops to smart phones. The emphasis remains on flexibility and usability.
For OEMs, the availability of pre-written code enables them to innovate without maintaining a large team of developers. “It’s good for the end-user. It’s good for the OEM. It’s just cutting out a lot of the drudgery,” says John Kowal, director of business development, B&R Industrial Automation (Roswell, Georgia). “So tasks like file handling, access control, things that you previously had to program every time, now you don’t. You can reuse these objects and focus your time where you bring value.”
OEMs can write their own code, they can start with the pre-written function blocks and add on, or they can do a mix of the two. Getting better product to market faster is only one benefit, he observes. “Your engineering assets are becoming more and more invaluable. They’re harder to replace. So if you can get the most out of your current engineering staff and, hopefully, make their lives easier, that makes it easier to retain them, to keep them motivated.”
These are just some of the factors that have led to change throughout industry. Now let’s explore what their affect has been on the application side.
Performance coupled with ease-of-use has enabled motion control to gain a foothold in applications traditionally dominated by hydraulics, pneumatics, and even induction motors coupled with cams. In timber processing, for example, introducing servomotors has dramatically boosted productivity.
When harvested logs reach the mill, they first get debarked, then go through a rough saw step in which the clean log is cut into planks. Positioning flexibility is important, since not all logs are straight. There also may be some positioning error when they are loaded into the saw. The saw blade needs to adjust to compensate for any skew. The finer the adjustment, the greater the amount of usable wood that can be produced from each log.
A major wood processor saw an opportunity to improve output by switching from mechanical shafting to motion control for the rough-saw step. The mechanical system could change blade position by ±15°. The servo-motor-based system cuts that to ±3°. The station went from processing 45 boards per minute to 75 boards per minute. It also produced more high-value lumber from each log (see Figure 1). “With the old system, they could get as low as 50% yield from a log,” says Michael Miller, manager of regional motion engineering, Yaskawa America (Waukegan, Illinois).
Wind turbines are of growing importance in a world focused on clean energy. Servo motor systems have been used to adjust the position of the vanes to best extract energy from oncoming gusts. One of the issues with wind turbines is that the constant buffeting rotates the upper assembly azimuthally. This causes wear over time, compromising performance and necessitating expensive and difficult maintenance operations. A yaw control system based on servo drives helps control this motion. It features encapsulated electronics and can tolerate vibrations as high as 1G (see Figure 2).
Similarly, the marine sector has begun taking advantage of electromechanical solutions. It started with using the variable-frequency drives on shipboard pumps and compressors. Although this is not motion control, it does represent an entry point for electronic motor control. More recently, servo motors have begun to see use in leveling and stabilization systems for smaller vessels like yachts. These active stabilization systems are designed to compensate for rough seas, using feedback to keep the deck as stable as possible.
In both applications, motors and drives need to be rugged enough to tolerate moisture, heat, and vibration without premature failure. They need to be straightforward to integrate into the system and to maintain. That’s where some of the benefits described above pay off.
The improvements over the past few years have made a big difference in manufacturing. The machine-tool sector has traditionally been a strong application area for motion control. CNC equipment like laser cutting, water-jet cutting, and plasma cutting machines need to move as smoothly as possible along the motion path. That’s where the latest-generation feedback devices, coupled with adaptive tuning and control algorithms have significantly improved part quality.
“It’s all about information,” says Carlberg. “Say you have a 24-bit encoder. You can’t position to one-sixteenth-millionth of a revolution but having all that information makes your tuning loop so much tighter that the amount of error is much less. We’ve actually measured that the motors run 20° cooler than they did in the previous generation, just from the reduced error.”
For point-to-point motion, it’s not a question of path smoothness but of how quickly the load can arrive at the destination and settle without overshoot or ringing. Here, too, the technology demonstrates significant improvement. Miller describes a customer who retrofit their pick-and-place system to reduce settling time from 50 ms to 4 ms. The change increased part count for a revenue bump of $29.24 per hour. That may not sound like much but over the course of the year, it adds up to better than $140,000 USD.
There was a time when prototyping was a lengthy, expensive process that required skilled machinists to assemble each part. Today, that prototype is just as likely to be fabricated using 3-D printing. 3-D printing involves heating some form of plastic or polymer and extruding it to build a shape layer by layer. Depending on the size and complexity of the part, the process can take hours or even days.
Effective motion for 3-D printing needs both smooth paths during material deposition and rapid point-to-point moves with minimal settling time when the extruder head moves to a new position. Early versions of the machines were based on stepper motors. As projects become more sophisticated, however, demands are changing. “3-D printing machines are growing up from stepper motors to servo motors so they can have better performance, better repeatability, and longer lifetimes,” says Miller.
“Companies are moving beyond just using 3-D printing to make prototypes,” says Carlberg. “The technology is evolving so quickly that people are starting to think about using it for actually making production parts. I think the servo technology that’s available today is part of the reason all these advances are happening in 3-D printing”.
Decreasing settling time allows the extruder head to move more rapidly from one point to the next position where will begin depositing material. Over the course of a multi-day run, shaving even a few milliseconds off of each move can have a dramatic effect.
New Routes to Motion
Manufacturing automation used to focus on making a lot of the same thing very efficiently. Today, the effort is centered around customization. Here, smart conveyor systems play a key role as manufacturing nudges ever closer to the elusive “batch of one.” A smart conveyor system consists of autonomous carts running on preconfigured tracks. In a sense, the elements of a motor are split between the two. The tracks contain the motor coils while the cards incorporate permanent magnets. Selectively energizing the tracks moves the carts to varying positions at different speeds and with different cart-to-cart spacings.
ARUP Laboratories, part of the University of Utah Department of Pathology, specializes in clinical diagnostics. It offers an array of 3000 different combinations of tests. Serving hospitals, clinics, and laboratories across the United States, it has a two-story refrigerator that can store up to 2.3 million specimens. It uses an intelligent conveyor system with more than 200 m of track to enable it to process up to 6000 samples per hour (see Figure 3).
Each specimen is placed in a magnetic “puck.” Each meter of track contains 60 motor coils. When activated, they move the parks around the lab to go through their various steps including thawing, preparation, testing, etc.
For this type of application, identifying, tracking, and properly routing the samples is essential. “They bind the test specimen to one of these moving carts and they have a complete routing history of the test sample through their diagnostic lab,” says Neil Bentley, MagneMotion product line manager at Rockwell Automation (Devens, Massachusetts]). “They were getting ready to do a major upgrade and they were looking to improve the quality of their process. For them, that routing history of the sample was really important.”
Intelligent conveyor systems have a variety of uses for parts handling in manufacturing and assembly. They can also be used in packaging, for example to build packages of mixed cold cuts or cosmetics kits.
Determinism and traceability are likewise issues in life sciences metrology for applications like DNA sequencing, visual pathology, and cellular imaging. In these cases, samples are imaged and analyzed using techniques such as laser line scanning and spectroscopy. In digital pathology, for example, the system takes a series of images of the sample and stitches them together into a single image that the radiologist can review. Positioning needs to be highly accurate to ensure effective image capture. At the same time, it needs to take place quickly.
Because of the move-and-settle nature of the process, this type of equipment has traditionally used stepper motors. Now, as with 3-D printing, that is changing. “One of the big trends we are seeing is a move from stepper motor technology to servo motor technology,” says Brian Handerhan, business development manager at Parker Hannifin (Irwin, Pennsylvania). “It may be driven by speed and throughput requirements where they are doing imaging on the fly, or it is still move and settle but using very-high-resolution encoders to cut settling time.”
Another part of that trend is the shift from standard servo motors to direct-drive motors, whether rotary or linear. These frameless, or kit motors minimize footprint and reduce compliance. Because of the form factor and flexibility, they give OEMs more flexibility to differentiate their equipment from similar offerings on the market.
Like Miller, he points to the value of auto-tuning and feedback in reducing settling time. This holds for not only life sciences but other metrology applications such as semiconductor test and wafer mapping. “You’re talking about making moves of less than 100 µm, with a stability of ±10 nm and doing that in less than 50 µs,” says Handerhan. For many years, air bearings were the technology of choice for these applications. Leveraging sensory input and feedback with improved software tools has allowed mechanical bearings to regain market share.
Probably the biggest overall trend in applications across the board is a growing realization of the value of intelligent assets. Combining smart components, industrial networking, and software to make sense of it all open the way to predictive maintenance, faster changeover’s, lower cost of operations through energy analytics, fewer headaches for staff and management alike.
The technology is available; end-users just need to take advantage of it. “We are in the beginning phases of the journey,” says Jim Grosskreuz, global product manager in the Kinetix motion business at Rockwell Automation (Mequon, Wisconsin). “There is room to pull intelligence together in a more meaningful way than what is being done today. I think that large end users are starting to understand now the value that can bring.”
Thanks go to Adam Moos, product sales manager, Parker Hannifin, for useful input.