Integrated Servos Achieve 1-Micron Repeatability in Atomic Force Microscope

When designing a scanning motion system for an atomic force microscope (AFM), engineers typically assume that achieving micron-level measurement sensitivity requires the most complex, expensive motion architecture available. For a recent project involving a semiconductor-style stage with a granite base, the engineering team at Bell-Everman faced a critical decision: stick to a conventional, non-integrated servo system with complex secondary feedback, or test a "value-engineered" approach using integrated servo motors.

Bell-Everman designs and manufactures high-performance linear and rotary stages for OEM machine builders. To ensure they met the client’s strict specifications, the company maintained "two paths to success,” both of which utilized Teknic motion control technology and a zero-backlash screw. The first path employed a high-end architecture: Teknic’s Hudson brushless motors paired with external Eclipse servo drives and a third-party linear encoder for dual-loop control. The second path utilized Teknic’s ClearPath integrated servos, relying solely on the motor’s internal encoder for single-loop control.

The team anticipated that the separate component architecture, with its dedicated drives and linear scale, would be the ultimate solution for precision. However, the testing phase revealed a surprise regarding the integrated ClearPath capability.

"We ended up scrapping the whole high-end fork of this development because our screw and a ClearPath servo was able to do 1-micron bidirectional repeatability," says Mike Everman, Bell-Everman's CTO and President.

By pairing the mechanical advantage of a 5mm ball screw with the high-resolution feedback inherent in the ClearPath brushless servo system, the machine achieved exceptional positioning accuracy without the cost or complexity of a linear scale.

"The value-engineered machine blew the doors off of what they thought they needed on the high-end machine," Mike notes. "We’ve let the [more complex] architecture die on the vine because this came out so great."

Beyond positioning accuracy, atomic force microscopes are hypersensitive to electrical noise. Standard servo configurations, which involve long cable runs carrying high-frequency signals between motors and amplifiers, generate Electromagnetic Interference (EMI) that can disrupt delicate sensors.

Mike reports that the AFM customer was "blown away at how electrically quiet" the integrated system was. Because the ClearPath architecture houses the drive electronics directly inside the motor’s aluminum and steel housing, the body of the motor acts as a shield.

Mike explains, "Having all of the drive electronics inside of the same Faraday cage as the motor itself... has just turned it into this electrically dead quiet system,” adding that the customer is "so impressed with how electrically quiet it is."

Validating a simplified, integrated motor for such a sensitive application required rigorous testing, but it also required trust in the component's engineering specifications. While Bell-Everman typically handles motor sizing themselves, they rely on Teknic’s engineering support when navigating these highly challenging designs.

"If it’s hairy edge... I’d much rather work with Teknic’s application engineers, and the response is fantastic," says Mike, referring to applications that push thermal or torque limits.

This 20+ year partnership allows Bell-Everman to confidently deploy "value-engineered" solutions like the AFM stage without risking performance. Mike notes that he leans on the Teknic team for simulation and feasibility analysis, stating, "I don’t know of any other motor and drive vendor that I’ve worked with that’s provided so much engineering expertise and has been so easy to work with."