Direct-drive technology outperforms traditional motion control systems

Replacing a traditional motion control system with direct-drive technology improves efficiency and design flexibility.

By Steve Feketa and David Hansen

Let’s face it — under trying economic times, you look for any competitive advantage that improves your margins and adds money to the bottom line. A good place to investigate is with machine design. Simplified machines with fewer components that run more efficiently are gaining positive reviews. Better yet, they’re cheaper to build. With a lower total cost of ownership and a quicker return on investment, these innovative, flexible machines are useful investments.

Unfortunately, older rotary and linear motion actuation technologies like gearboxes, transmissions, rack-and-pinion actuation or belt-driven actuators can stand in the way for machine builders who want to take machine design efficiencies to the next level. For example, gearboxes and transmissions used on rotary motors produce torsional deflection of the mechanical components. This effectively adds a spring to the system and generates backlash when the motor temporarily decouples from the load, particularly during a change in direction.

Mechanical power transmission devices, such as ballscrews and belt drives (used in linear motion applications) or precision gearheads (used in rotary motion applications), are constructed with components that wear. This can lead to performance degradation and eventual system failure. These components may require adjustment, lubrication and tensioning, resulting in production downtime. They also introduce backlash (clearances between mating components) and compliance (component deflection) into the servo system, making it more difficult to tune and measurably slower in achieving the desired positioning.

The direct-drive alternative

Direct-drive rotary and linear motion technologies can help overcome many of the drawbacks associated with traditional mechanical machine designs. In the past, direct-drive solutions were cost-prohibitive for mainstream industrial applications. However, the technology is now available at a reasonable price — and the benefits could help you capture your ROI faster than ever before.

Direct-drive technology is mounted to the payload, which eliminates the need for a gearbox.

– Steve Feketa and David Hansen

If your manufacturing process involves directional changes in machinery components, gearbox systems require the motor to decouple from the load momentarily, during which any set tuning variables are rendered irrelevant. As a result, the machine’s precision drops significantly, leaving it free to produce scrap or diminish its throughput potential.

Direct-drive technology is mounted more directly to the payload, which eliminates the need for a gearbox. Therefore, it reduces compliance and backlash problems, and provides improved overall system control. As a result, direct-drive systems have faster settling times, which can help reduce scrap and improve the machine’s throughput.

Improved efficiency

Traditional motion control systems that rely on mechanical transmission components waste power in the form of heat, friction and noise. In fact, even a brand new precision servo-rated gearhead is at best 90% to 95% efficient on average. Direct-drive technology practically eliminates the three forms of lost power, which often allows the use of a smaller motor and drive that requires less electrical current.

Direct drives also can eliminate the need for pneumatic or hydraulic systems, two of the most expensive sources of energy in a factory. Matching a direct drive with a servo or brushless AC motor avoids the significant energy losses associated with pneumatic air leaks and the high recycling costs associated with hydraulic fluids.

Simplified mechanics

Because direct-drive technology eliminates wear components, such as radial bearings, ballscrew nuts and pinions, belts, racks and gearboxes, machines can be more reliable and provide more stable, long-term accuracy. Because there are fewer parts that require ongoing maintenance, you may also enjoy increased productivity and reduced scrap, and reduce the number of spare parts kept on-hand.

These simplified direct-drive systems also have a smaller machine footprint and reduced assembly time, which can save significant time and money during installation.

Improved flexibility

Inflexible machines designed for specific tasks often use cams, linkages or rodless pneumatic cylinders for motion control. However, the simplest changes in scope can require significant amounts of time to retrofit. Linear motors with direct-drive configuration can provide the same high acceleration and speed associated with cams, linkages and other two-point motion devices. However, linear motors also are capable of multiple positioning points via programming changes and therefore are much easier to reconfigure for process changes.

Numerous industries have embraced direct-drive technology. In the consumer packaged goods (CPG) industry, for example, direct-drive linear motors coupled to high-precision linear encoders provide more precise fill volumes. With repeatability in the two to three micron range, it improves margins by minimizing the free goods being shipped out the door. In addition, the high precision reduces the need for any secondary operations like sorting or trimming that results from inconsistent manufacturing processes.

A manufacturer of airfoils replaced a belt-driven system on a large-format gantry with a system based on linear motors. Reducing the belt-driven system’s inherent settling time increased throughput by almost a third.

Similarly, direct-drive technology coupled with servomotors eliminates the line shafts commonly used to power machines. By replacing the line shaft with several individual servomotors powering each specific piece of its manufacturing process, one packaging machinery manufacturer realized a 20% reduction in energy losses. The company also was able to achieve tighter tolerances, which reduced accumulated error and associated scrap with less time spent maintaining the packaging equipment machinery.

Value for all

While innovative machine design isn’t a new concept, it also isn’t an option anymore — it’s an economic imperative. Simplified machines design and a lower total cost of ownership is appealing in this down economy and in the future, when tighter margins demand differentiation between you and your competition.

Optimize your mechanical designs from the start and become more competitive. Direct-drive technology helps build higher performance machines that run on less energy, are easier to maintain and are quicker to update for product or design changes — all at the same or lower cost as machines built with traditional motion control systems.

Steve Feketa is the global product manager, linear motors and stages at Rockwell Automation. David Hansen is global product manager, Kinetix motion control at Rockwell Automation.

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