How Self-Balancing Centrifuge Rotor Technology Works

With the invention of the centrifuge came the problem of rotor balance. Specimen containers must be properly sized and properly located on the rotor to provide rotor balance each and every cycle.

By Gary Howell

Problem: With the invention of the centrifuge came the problem of rotor balance. Specimen containers must be properly sized and properly located on the rotor to provide rotor balance each and every cycle. Rotor balance is achieved by symmetrically placing opposing size and weight specimens on the rotors as they are loaded. Within this standard rotor-load procedure, an uneven number of sample containers cannot be centrifuged as this creates out-of-balance rotors.

Similarly, an even number of specimen containers, but with unequal mass, such as 5 and 10ml samples, cannot be centrifuged in a single centrifuge cycle. This also creates out-of-balance rotors that can damage the centrifuge or cause it to shut down. Centrifuge operators and robotics software must be aware and trained to avoid these day-to-day realworld sample processing restrictions. Centrifuging a single microtiter plate or blood bag is presently out of the question without installing dummy counterweight containers.

These sample handling process limitations have created commonplace workarounds in the laboratory including: avoiding odd-numbered specimen cycles; use of a single specimen container size within a laboratory operation; use of dummy specimen counterweights; operator training for balanced rotor loads; and process bottlenecks to satisfy one or more of these conditions.

A general solution permitting any sample at any time would allow clinical and analytical laboratories to provide more efficient sampling handling, thus lowering the cost of services and increasing profit margin. Hospitals and clinics embracing a general solution as well as manufacturers providing the technological solution would enjoy competitive advantages over those who do not.

Solution: A newly patented technology, called Rotor-Mate™, provides a powerful transparent solution to the aforementioned problem. Centrifuge rotors are typically designed and mounted with their center of geometry coincident with rotation and mass centers. The rotor spins about this center without vibration. But any eccentric rotor load, such as a single specimen container, causes the rotor’s fixed center of geometry and rotation to be at variance with its new center of mass and vibration ensues. Rotor-Mate solves this problem by allowing the rotor to physically shift its geometric center and rotate about the new center of mass in proportion to the eccentric mass. In so doing, the rotor operates totally smooth, even with enormous out-of-balance eccentric loads such as specimen serial loading or single microtiter plates.

The practical result is to free the operator or robot to process specimens of various sizes and in odd quantities without regard to specimen balance. Existing centrifuge manufactures have some form of rotor imbalance management, but none tolerates an imbalance in excess of 200 grams, as does Rotor-Mate™, or do so automatically, instantly and without electronics.

Rotor-Mate™ is scalable up/down for large and small centrifuge rotors and is devoid of springs, elastomers and sensors. Rotor-Mate™ is currently available for commercial application exclusive and non-exclusive licenses in both clinical and analytical applications.

To see this technology in action, search “rotor-mate4m” at

Categories: How it Works

Published In

Scientists & The Social Media Magazine Issue Cover
Scientists & The Social Media

Published: April 1, 2011

Cover Story

Scientists & the Social Media

Laboratories are at the forefront of research and analysis. But when it comes to communication, they are followers rather than leaders and can be very slow to adopt innovations.