Precision Assembly Stages: Upgrading from AC Induction Motors to Servos

For engineers designing high-speed automated assembly lines, the difference between a standard AC induction motor and a modern servo system often dictates the throughput of the entire machine. "The cycling performance of the servo motor is far and away better than what we can achieve with the AC motor," says Bill Nott, Application Engineer at Stelron.

Stelron specializes in designing and manufacturing precision motion systems, including the Precision Link Chassis (P-Link) and Rotary Assembly Dial (RAD) index tables. These platforms are the backbone of their customer’s automated manufacturing lines, used extensively in packaging, medical device assembly, and industrial processing. To maximize throughput in these applications, the motor driving the input shaft must provide precise control over the index and dwell cycles.

Historically, Stelron relied on commercial AC induction motors paired with variable frequency drives (VFDs) to power its chassis. While functional, this setup introduced complexity when precise cycling was required. Achieving a specific index-and-dwell motion profile often necessitated external feedback devices.

"With the AC setup, I have to worry about acquiring a sensor to simulate that it's [in] dwell and then stopping it," Bill explains.

By switching to Teknic’s ClearPath integrated servos, Stelron eliminated the need for these external sensors. ClearPath combines the brushless servo motor, encoder, drive, and controller into a single compact package. Because the motion profiles are handled internally by the servo's controller, the positioning is exact and repeatable without requiring a PLC to manage external sensor triggers.

"It's directly programmed into the servo move," Bill notes. This transition has allowed Stelron to offer tighter control over its conveyor indexing. The shift in performance was significant enough that one of Stelron’s customers—a major global pharmaceutical and medical device manufacturer—"lock, stock and barrel switched out all the AC inverters in lieu of Teknic NEMA56 [servo motors]."

Beyond simple motion control, the switch to servo technology provided Stelron with a new window into their machine mechanics. The ClearPath MSP (Motor Setup Program) software includes a built-in digital oscilloscope and a suite of diagnostic tools that allows users to visualize performance data such as torque, velocity, and tracking error in real-time.

For Bill, this data is vital not just for tuning the motor, but for diagnosing the mechanical health of the assembly line itself. "We always scope the motor," says Bill. "We have been able to look at the gross information coming out of the scope to be able to target some downstream mechanical issues."

By analyzing the torque feedback, Stelron can identify binding or resistance in the various mechanical linkages, ensuring the system runs smoothly before it leaves the factory floor.

Stelron integrates various ClearPath motor sizes depending on the specific machine requirements. They typically utilize the NEMA 56C AC-input motors for their heavy-duty Precision Link (P-Link) chassis, while deploying NEMA 23 or 34 DC-input motors for the Rotary Assembly Dial (RAD) systems.

"I love the little DC motor," Bill says, noting that the NEMA 34 ClearPath is "a great substitution for a traditional permanent magnet DC motor with an SCR [Silicon-Controlled Rectifier] drive."

Regardless of the frame size, the software interface and ease-of-use remain primary drivers for the engineering team. The ability to connect a PC and immediately test the mechanics streamlines the factory acceptance process. "The ease of being able to drive it right from the graphical screen from MSP is what sold me on using the product," Bill explains. "I just plug the laptop into it and I can run it straight from the laptop."

This combination of performance and usability has made Teknic the preferred standard for Stelron's designs. Bill concludes, "We try to push Teknic wherever we can and we love the products."