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What You Should Know About Frameless Motors

12 Jul 2021
Tom S Wood

What exactly is a frameless motor?

A frameless motor is the active torque and speed producing part of a conventional motor, but without the shaft, bearings, housing or endbells. The frameless motor consists of only two parts: the rotor and stator. The rotor is usually the inner part, consisting of a rotating steel donut assembly with permanent magnets, that mounts directly onto your machine shaft. The stator is the outer part, with steel laminations and copper windings around the teeth to create the electromagnetic forces that mounts compactly within the body of your machine housing.

KBM™ Series Frameless Motors

Why should I use frameless motors?

Frameless motors are generally designed into advanced machines that would benefit from one or more of the following:

  • Increased machine performance
    • No mechanical compliance (no backlash, no lost motion)
    • Higher system bandwidth
    • Improved machine efficiency
  • A more compact form factor
    • Smaller machine footprint
    • Highest torque per volume
  • Reduced maintenance
    • Fewer mechanical parts
    • No components subject to wear or maintenance

How do I size a frameless motor for my machine application?

Frameless motors are sized the same way that you might size a conventional, housed servo motor. The machine application is evaluated for the motion requirements for both torque and speed. A machine designed with a frameless motor will generally have higher efficiency due to the lack of gearing, belts and pulleys, or coupling elements in the mechanical drive train. This efficiency often simplifies frameless motor sizing. Knowing the actual machine or part duty cycle timing generally gets you the RMS torque and speed as well as the peak conditions needed to select a motor. There are online motion sizing tools available to help you properly calculate your motor sizing requirements.

There is also a frameless motor performance curve tool that allows machine designers to understand actual motor and drive performance, even at different bus voltages, available drive current, and ambient temperature limitations. This tool helps you optimize the choice of frameless motor winding based on actual machine requirements rather than choosing from a limited set of windings based on standard input bus voltage.

Which applications are best suited for frameless motors?

Frameless motors are broadly used across virtually all machine markets: robotics, medical, machine tool, packaging, printing, converting and general automation. Basically, anywhere the benefits of improved machine performance, compact form and reduced maintenance are valued.

How easy is it to install a frameless motor?

Most people assume that the installation of a frameless motor is a complex and daunting task. A quick review of this “how-to” installation video will help to dispel those concerns. Typically, frameless motor components can be installed in a basic machine housing design using slip-fit tolerancing and readily available industrial adhesives. The use of frameless motor part sets often leads to improved manufacturability and reduced machine setup times through the elimination of couplings, gearing and belt adjustments. Also, system tuning and commissioning time is reduced due to increased repeatability of the system mechanics.

Kollmorgen provides frameless motor solutions in 17 standard frame sizes (60 mm to 850 mm diameter, with torque up to 13,000 Nm), each with multiple stack lengths and winding options. These standard designs can provide your machine with an ideal-fit frameless motor solution optimized for your application.

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About the Author

Tom S Wood

Tom S Wood - Author

Tom S. Wood, a 30+ year veteran in high performance motion control has integrated motion control solutions as a machine designer, servo customer, manufacturer’s representative, High-Tech distributor, and as a Kollmorgen Motion Control Product Specialist. When not playing with custom servo motors, Tom enjoys biblical coins, wood turning, and playing sports with his two grandsons. Tom may be contacted at [email protected].

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