Inductive Linear-Position Sensor/Limit-Sensor Units

Marshall Space Flight Center, Alabama

Monday, October 01 2007

These non-contact devices afford more information than do mechanical limit switches.

A new sensor (see figure) provides an absolute position measurement. The figure presents a schematic view of a motorized linear- translation stage that contains, at each end, an electronic unit that functions as both (1) a non-contact sensor that measures the absolute position of the stage and (2) a non-contact equivalent of a limit switch that is tripped when the stage reaches the nominal limit position. The need for such an absolute linear position-sensor/ limit-sensor unit arises in the case of a linear-translation stage that is part of a larger system in which the actual stopping position of the stage (relative to the nominal limit position) must be known. Because inertia inevitably causes the stage to run somewhat past the nominal limit position, tripping of a standard limit switch or other limit sensor does not provide the required indication of the actual stopping position. This innovative sensor unit operates on an electromagnetic-induction principle similar to that of linear variable differential transformers (LVDTs).

Depending upon the application, this sensor technology can provide absolute position in various forms and can easily be integrated into users’ designs. The basic sensor utilizes only two active inexpensive components. The sensor can be placed on an adhesive surface, or could be buried inside or underneath the outer skin of a component. The sensor technology can be physically scaled up or down and can even be employed inside a microelectromechanical-system (MEMS) device. The sensor can be designed with redundant sensor coils without additional physical volume.

In testing, the sensor produced accuracies of 4 μm, and greater accuracies are possible with other sensor configurations. The sensor can use excitation frequencies ranging from several kilohertz to the megahertz region. The sensor is extremely repeatable with data correlations of 0.99999 or greater. This simple sensor technology has been patented and is available for licensing opportunities.

This work was done by Dean Alhorn, David Howard, and Dennis Smith of Marshall Space Flight Center and Kenneth Dutton of Sverdrup Technology, Inc.

This invention has been patented by NASA (U.S. Patent No. 7,116,098). Inquiries concerning nonexclusive or exclusive license for its commercial development should be addressed to Sammy Nabors, MSFC Commercialization Assistance Lead, at This e-mail address is being protected from spambots. You need JavaScript enabled to view it . Refer to MFS-32192-1.