Monday, March 26, 2012

Coffee Chat: Join the Chain [ Actuation ] Gang

KEEPING A LOW PROFILE LoPro is our signature product line of linear actuators based on DualVee Motion Technology — pre-engineered units we launched in the mid-1990s in response to an increasing demand from our customers looking for long-length actuation. It's a super versatile linear motion solution that comes in custom lengths and a variety of actuation types. Namely, chain, lead screw, ball screw and belt drives.

For today's coffee chat, we wanted to focus on chain actuation — an option that makes us stand out in the industry because it's not widely offered in the linear motion market, according to our Project Engineer Brian Burke. Why chain actuators are not more commonly offered is a good question, but in this edition we've focus on the pros and cons of chain actuation, how it works and for what applications it works best.

PRODUCT OF ENVIRONMENT One main challenge for any actuator is how it stands up to contaminants, whether small and soft or large and gritty, aluminum chips or sawdust, Burke said. Some actuators grind to a halt when debris builds up in the guide and drive systems. The chain changes all that.

"LoPro is especially well suited for reliable operation in these extremely contaminated environments when configured with the chain drive option," Burke said.

Chain and sprocket drives work excellently in very dirty environments because the sprocket teeth fling away debris from the chain gaps, he explained. If contaminants start to build up at the sprockets inside the drive and idler ends, however, the chain can start conveying that debris. To make sure it doesn't, LoPro units come with an open bottom drive and idler ends to let the particles just fall through instead of accumulating.

SIZING IT UP All five LoPro sizes can come with chain actuation, Burke said, although lot of times, people choose the chain-drive actuators to hoist huge loads or carry them across pretty long lengths. From the roller chain #25 on the smallest through the #50 on our largest unit — all of which come with either carbon steel or corrosion-resistant stainless steel chain, sprockets, fasteners and bearings.

Since LoPro units are basically heavier duty when outfitted with chain actuation, they're normally manufactured in lengths that surpass the capability of ball screw-driven actuators, Burke said. By the way, remember that [ infographic we made that compared ball and lead screw actuation ]?

Ball screw actuators don't normally travel more than 96 inches, which for a chain-actuated drive, that length isn't an issue at all. But if the required travel length is longer than that, say around 600 inches, the best bet isn't chain but an AT belt drive, Burke said. If it's that long, the chain starts to drag inside the LoPro when positioned horizontally. Since chain is high-tensile, it works well for vertical applications, like lifting, he said. At least that way, the chain won't sag.

THE CONS Of course, there is a downside to every option — it's all a question of application requirements. For one thing, the metal-on-metal friction between drive sprockets and chain means it needs lots of lubrication to prevent wear and tear and eventual failure. The metallic grinding also means chain-driven rails get pretty noisy compared to other drive options.

Chain also gets stretched out over its usable life, Burke said. So it has to be adjusted after its first use and then periodically to make sure it performs well. And though they're great if moving in one direction, chain drives get a lot of backlash if they're bi-directional. Backlash means less linear accuracy compared to other drive options.

CIRCLING BACK AROUND LoPro units driven by chain actuation have many advantages over other drive options, Burke said, especially for dirty environments and long travel lengths. With enough maintenance and lubrication, chain drives can perform well for years. They're not meant for highly accurate applications because of possible stretching and the backlash, but they're great for vertical lifting functions. As we said earlier, it's all a matter of application specifics.

MOTION MONDAY CHALLENGE Since it's #MotionMonday, we're turning this into a game. This time, since we got a little wordy, we've concocted a crossword challenge to test your reading retention. The first 10 people to email the correctly answered puzzle will get some fancy BWC swag. You ready for this? Let's go!

[ Download the puzzle here ]