Technology improvements continue in linear motion design, with packaging and medical leading the charge this year. In fact, the biggest trend has been more reliance on flexible machine designs, which require that machine axes constructed for one purpose easily reprogram for others.
“Flexible machine designs—ones that engineers can reconstitute for multiple functions—are what machine builders want today. Industries in which such designs are prevalent include packaging, material handling, converting and factory automation,” said Dave Hein, VP of engineering at Nexen.
“Each industry has different individual needs, but the common thread is more machines to deliver flexible performance.”
For example, a case-packing machine in the packaging industry today might need to pack 4, 8 or 16 cartons on the fly. The demand for flexible machine designs has driven implementation of programmable, flexible machine axes for such tasks, added Hein.
Trending mechanical changes in linear design
On the level of motion subcomponents, Rick Wood, managing director of Rollon, sees some of the following advances leading linear rail and actuator trends.
• Today’s tight motion controls and high servo-encoder counts mean some linear actuators can hold acceptable repeatability with a servo and belt drive, sans linear encoder.
Manufacturers today also integrate drives and controls for seamless machine integration (to take some of the “black magic” out of electromechanical motion). That’s according to Jeremy Miller, product manager for linear mechanics at the Electromechanical Div. of Parker Hannifin.
• Some of today’s linear rails can carry high loads, even when slightly misaligned. In addition, some of today’s telescopic linear guides carry heavy loads with minimal deflection. They make long strokes and resolve misalignment from poorly mating components and nonparallel surfaces. Rollon’s offerings here abound. The rails mount to uneven surfaces and function in imperfect environments—for example, on large rollers passing on steel raceways.
In a similar way, mechanical gearing that doesn’t rely on backlash to function is addressing other traditional design limitations. “This functionality lets mechanical designers create machines that deliver higher precision in reversing applications, while also giving servodrive programmers more flexibility in choosing system operating gains,” said Hein.
• Some belt-driven linear actuators have universal drive ends to be field-configurable. The motor or gearbox installs on either actuator end. Pre-tensioned belts and a stiff monorail can deliver high load capacity and thrust force with repeatability to 0.002 in., according to Wood. So, say a machine builder must move gearing and motor horizontally on a linear actuator to accommodate a machine change. Instead of spending hundreds of dollars to ship the actuator back to the manufacturer for rework, the builder can just remount the motor to the actuator’s other end using a universal drive head—for an actuator reconfigured in 15 minutes or so.
• There have been improvements in raw materials (steels, aluminum alloys, ceramics, engineered polymers and performance elastomers) for manufacturing linear rails and actuators. So, some manufacturers now skip some of the grinding of linear guides and leverage tighter raw-material specifications.
In addition, zone hardening on working surfaces lets manufacturers use inductive processes instead of baking whole parts in an oven. Specialized aluminum extrusions can also make linear-actuator bases straighter and flatter than standard extrusions. This in turn makes installation pulleys, belts and linear rails faster and less expensive, for shorter lead times overall.
Industries spurring linear motion design changes
The defense industry still demands new linear-motion systems all the time, especially those with very low friction. Other growth industries for motor-driven slides are those needing washdown components for food and beverage and medical applications. Here, FDA-compliant washdown slides are stainless to resist caustic foams of chlorine.
Tubular linear motors, according to Miller, come with an IP67 rating standard, so survive such washdown environments.
“The food and beverage industry demands corrosion-resistant linear products and enclosed actuators impervious to washdown cycles,” said Wood. For these types of applications, his engineering staff recommends corrosion-resistant platings that withstand real-world equivalents of up to 750 hours of salt-spray fog testing.
“Aerospace, biomedical, medical and 3D printing designs are driving improvements more than most other industries,” Wood added.
IoT and linear motors in linear-motion systems
Another trend is that many companies are developing Industry 4.0 components applicable to enterprise-level connectivity. However, there’s a major catch.
“Determining features that make a specific component (such as a motor or gearbox) useful for 4.0 application is still a type of analysis in its infancy. Over the next several years, some features and functions will become more common and standard … while others will stay machine or function specific,” said Hein.
In contrast, the proliferation of linear systems using linear motors continues unabated, and it’s no longer just for expensive machinery. As more linear-motor manufacturers work to make their linear alternatives simpler to integrate—even as drop-in replacements for traditional fluid-power actuators—more OEMs are putting them on even standard axes. The catch here is that such linear motors must satisfy ISO standards for mounting and footprint, noted Miller. Only then do they reduce design complexity for OEMs and users.
That said, some linear motors provide an alternative to even specific electromechanical designs. “Tube motors can eliminate the mechanical rotary-to-linear device and gearing of traditional linear setups. Plus they integrate much more tightly than traditional ballscrew or belt-driven cylinders for lower overall cost, design complexity and footprint,” said Miller. No moving bearings means they’re also maintenance free.
Miniaturization yet another linear-motion trend
In general, smaller machine footprints are always better. No wonder then than OEMs today want to downsize specific components and still maintain machine operating specifications.
“This goal of the machine designer has challenged Nexen to validate components robustly, under extreme operating conditions, to let application engineers confidently apply them,” said Hein.
Others agree, and note the difficulty in servicing tiny designs as a reason for robustness. “Over the past few years, we’ve seen moves toward miniaturization of applications that use bearing and linear-guide components,” said John Longo, general manager at IKO. In past decades, applications more commonly used linear-motion guides of size 15-mm (rail width) or larger … and medium sizes of cam-follower bearings, according to Longo.
“But in recent years, possibly with demand for smaller machine footprints, modules in machines and components have shrunk in size,” he said. So, smaller products in bearings and linear-motion guides are more interesting to design engineers than before.
As mentioned, the reduction in size also creates a need for easy maintenance and long component life, as sometimes it’s not as easy to do maintenance on smaller modules as it is on larger modules and components.
“IKO introduced the world’s smallest 1.4-mm-diameter cam followers in 2008, and 1-mm-width profile rail-type linear-motion guides in 2005,” said Longo. “Now IKO also offers expanded lines of a C-Lube maintenance-free product series in both linear-motion guides and rolling bearings.” These products are working in the field and in more design projects than ever before.
Trend toward integrated systems
More end users now buy pre-engineered linear setups … everything from linear actuators to Cartesian robots (to get more load capacity than SCARAs). However, getting complete systems can be difficult because some actuator manufacturers only offer one controller, said Wood.
Here, some common controls don’t have a suitable mechanical solution, are as expensive as a whole package, or demand that installers have prior knowledge of the control, electrical and mechanical setup. However, designers that buy separate guides, ballscrews, mounting surfaces, carriages and brackets leave the responsibility for alignment and integration to the engineer. So building smooth-functioning linear actuators that meets performance, price and schedule requirements is challenging, Wood said. For this reason, more companies than ever are steering technical staff to focus on core competencies and outsource integration
In short, engineering staffs are smaller than ever, and design engineers no longer have the time to involve themselves in all design aspects. So vendors now execute more engineering to let design engineers act as project managers.
Such engineers also want components and linear systems that plug into CAD models. So when the OEM engineer approves the vendor’s calculations and proposed design, the vendor makes a CAD of the design. Then the OEM puts the CAD file into a parent model to check fit, form, and function—adding CAD files until the full design’s parent CAD file is complete.