Traditional motion still having a ball

By Jason Christopher, Field Editor

TECHNOLOGY advances in motion and drives seem to be everywhere. Every facet of our industry reveals an innovation that promises never-been-seen-before performance compared to what it seeks to replace. Fortunately, manufacturers of the more traditional linear motion technologies haven’t been resting on their laurels. In fact, they’ve been busy improving their and our processes.

“We work with a lot of small manufacturing companies that have small budgets, but that doesn’t mean they have small expectations,” says Rick Lamb, president of SpecPlus Automation Consultants, an Indianapolis-based system integrator, specializing in turnkey automated control and information services, mostly for discrete parts manufacturing. “They come to us with performance targets and cost targets, and we need to meet both of them.”

Lamb believes the technology used doesn’t matter as much as its ability to meet the system criteria. “It doesn’t matter if it’s linear motors, servo-driven slides or a servo-pneumatic cylinder,” he adds. “We select the technology that can best help us get to where we need to be. This is true, both for the machine’s performance measures, as well as its cost. If a pneumatic cylinder or ball screw-driven slide can give customers the results their processes need, then there is no reason to even bother looking at a linear motor.”

Lamb isn’t the only person with these sentiments. While linear motors have some advantages, many machine builders and integrators report that traditional ball screws and fluid-powered servo systems still have much to offer.

Still the One
Linear motors have been around for many years, but this technology became readily available only in the past decade or so. It’s now gaining popularity, but not at the lightning pace some predicted. Linear motor manufacturers boast about phenomenal acceleration rates and final traverse speeds, but, in reality, traditional competition isn’t far behind.

For example, performance and cost factors both have improved. “Lead screw-based slides, 2 meters long, running 2 m/sec velocities, were an expensive dream just a few years ago,” says Tom Solon, PE, applications engineer at Kerk Motion Products. “Now, they’re available for $500. The linear motor has higher ultimate speed and accuracy, and might generate more force. But why spend five to 10 times more money, accommodate the much larger footprint, and use the necessary power if the lead screw solution is good enough?”

The questions Solon raises are good ones. Many of us have a “Tinker Toy” mentality and a desire to experiment with new technologies. We’re engineers, after all, but we also understand how our decisions affect the bottom line. It can be difficult to justify experimenting with newer technologies when the lower-risk choice might still exceed targeted performance requirements at a lower installed cost.

In short, they do work well. “The traditional rail and screw technologies are proven over time,” reminds Sheldon Prom, chief engineer at Komo Machine of Sauk Rapids, Minn. “These solutions have been fine-tuned and they consistently work well. Traditional methods, even when combined with new innovations in seals and coatings, often represent a low-risk/low-cost solution.”

	FIGURE 1: HONE IN ON PERFORMANCE
	ADVERTISEMENT Ball screw motion on the horizontal axis of this honing machine is allowing it to achieve speeds of 150 m/min while prolonging machine life, even in a harsh environment. Source: Sunnen Products

Likewise, for equivalent applications, linear motors still require a much higher initial investment. “They require far more energy for the similar motion, and, as a result, have secondary cooling requirements,” says Russ Jacobsmeyer, product design and development manager at Sunnen Products, a St. Louis-based manufacturer of bore sizing and finishing equipment. Jacobsmeyer recently helped Sunnen transform its product line using ball screw-driven motion. Its finishing equipment has axes reaching speeds of 150 m/min, while enabling machine life in excess of 30,000 hours at worst case loading conditions (See Figure 1).

For many manufacturing companies, where margins generally are slim and competition surely is fierce, not meeting performance requirements is a very serious issue. Capital equipment costs are significant, but lost production and failure to achieve payback targets often is a bigger issue. Risk aversion is a big reason why traditional technologies haven’t lost significant market share to linear motors.

Mature Advances Possible?
Despite their advantages, how do mature technologies, such as ball screw-driven slides, keep making performance enhancements? The answer has several parts.

“First is the availability of high-precision thread rolling (See Figure 2 below), which enables very accurate positioning and actuation at low costs,” says Solon. “With micron and submicron positioning accuracy and repeatability, new products can be brought to market that were previously not saleable.”