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Switched at Birth Servo - Motor Winding Nomenclature Explanied

21 Nov 2013
Hurley Gill

If you have been following along on our Evolution of Kollmorgen posts, you realize Hugo Unruh was one of the first to successfully commercialize frameless motor technology. What most people don't realize is that Kollmorgen's motor-drive phase identification standards (A, B, C) were based on these frameless motors. Now the issue at hand is both sides of a frameless motor typically look the same, except for the side where the wire leads exit.

Thus the lead exit side of the motors was used to reference the label identification of the phases with a Clockwise (C.W.) rotation looking into the lead exit end of the motor.

Stator - Lead Exit
Looking at the lead exit end

This C.W. rotation of the rotor, looking into the 'lead exit end', is of course Counter Clockwise (C.W.W.). looking into the shaft (torque end bell and/or mounting end) of most framed motors.

Stator - Opposite End
Looking at the torque endbell direction

This phasing convention: A,B,C with a C.W. rotation looking into the lead exit end, transferred over to Kollmorgen's standard housed motors looking into the motor's rear or connector end. However most of the world's motor manufacturers started with housed motors, with the natural C.W. rotation looking into the torque endbell, often using the same labels: A,B,C. In order to facilitate new drives and their introduction with phase labeling customized for phasing identification using the convention of a C.W. rotation looking into the torque endbell, Kollmorgen identified these phases as U,V,W. This minimized potential confusion between the two phase labeling conventions. To convert one convention to the other for Kollmorgen's rotary motors simply identify your desired convention with U = C, V = B, and W = A. When motor/drive phases are looked at in a straight line, you are switching the two outside leads.

Torque Endbell View
Looking at the torque endbell direction

This method of always switching the two outside leads, regardless of who manufactures the motor will always minimize confusion of which motor phases where switched months and years later; otherwise, one is faced with trying to remember if they switched the top two or the bottom two, and it makes a difference.

Always refer back to the Kollmorgen outline drawings for phasing. You can find out more details on the correct phasing for Kollmorgen motors, here.

About the Author

Hurley Gill

Hurley Gill is a senior application engineer at Kollmorgen. With over 40 years of expertise in the motion control and automation industry, he is often called upon to solve the toughest of application challenges for Kollmorgen customers. Hurley holds a B.S. degree in electrical and electronic engineering technology from Virginia Tech. When not focusing on motion control, Hurley enjoys data analysis, harmonics and building/rebuilding projects.

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