B6.3 - A Simple, Sturdy and Cheap Sensor for Distance and Force in Spatially Constrained Environments

SENSOR+TEST Conferences 2011
2011-06-07 - 2011-06-09
Proceedings SENSOR 2011
B6 - Dimensional Measurement
S. Eibl, D. Plohmann, G. Ackermann, C. Meurer, H. Möstl - Sensorik-Bayern GmbH, Regensburg (Germany), M. Huber, H. Steigerwald - Strategische Partnerschaft für Sensorik e.V., Regensburg (Germany)
319 - 320


Coil springs show a well-defined relation between externally applied force and spring length, the spring rate. Thus, if one of these parameters is known, the other parameter can be calculated easily. Measurement of either of these two parameters using intrinsic parameters, like DC and AC electric resistance, is not a new idea and bears the potential to turn the coil spring into a promising sensor. While the idea of making a coil spring sensor is old and the potential applications are promising, it has never been made into a working prototype. We have completed this last step and want to present our results hereon.
The complex part of the resistance, the inductance, is to a certain extent dependent on the physical form of the coil - deformations of the coil are reflected in a change of inductance. Effects like the proximity or the skin effect influence the electromagnetic behaviour of the coil spring in a complicated, but reproducible way and provide a basis for the determination of its length and therefore also the force it is subjected to, by probing its inductance.
To probe the resistance of the spring we use high frequency alternating current, in a way to best take advantage of the abovementioned effects and at the same time minimise sensibility to uptake of external electromagnetic radiation. With our partners we have developed a sensor prototype using the coil spring as an AC/DC resistance in an RLC circuit. Here we exploit the variation of resonance frequency in the circuit with change in AC/DC resistance of the spring.
Our solution provides a prototype of a simple, sturdy and cheap sensor for distance and force with a high potential of opening up a new field for sensoric solutions in spatially limited environments.