Contact-free electro-magnetic reactance based mechanical tension sensors
Authors:
Phillip Coerlin; Christian Leiser; Tobias Kitzler; Tobias Senkbeil;
Anatol Schwersenz; Sebastian Schwiertz
TRAFAG GmbH Sensors & Controls, Kelterstrasse 59, 72669 Unterensingen, Germany
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Abstract
Movement determines our life. Therefore it is substantially to know the forces we need to get in movement. Byelectro-magnetic stimulation of the bulk material in mechanical components like shafts and pull rods it is possible to conclude onto the mechanical tension situation. Through inductive sensors in a specific geometric constellation to the transmitter the sensor signals can be used to measure torsional moments or tensile and compressive stress.
The system integration of planar coil systems, magnetic flux conductorsand advanced calculation algorithm regarding the transmitter- and sensors signal results in an advanced contactless sensor adaptable for any mechanical stress measurements.
Due to the perfect laterally reversed arrangement of the sensor coils to the transmitter the stress strength can be recalculated into their components. Hereby arises a new contact-free sensor for numerous applications.
Figure 1.
Principle of the measurement
In shafts and rods without permanent magnetization the magnetic domains are in random orientation (Figure1.). With the rising strain the magnetic domains arrange more and more. Whereas compressive and tensile strain leads to common mode orientation to the force axis torque moments will result in ascrew-line arrangement.
The stimulation with an alternating magnetic field leads to a response of the domains. These responseswill be measured simultaneously by quadrant-sensors. With the measurement of the four signals and calculation in the implemented electronic the strain is determinate.
In Figure2- Figure5 is shown how the different stress situations e.g.in a shaft can result in different arrangements of the magnetic domains.
Orientation of the magnetic domains without torque, compressive ortensile stress.
Figure2.
Change in the orientation of the magnetic domains under compressive stress. (Common Mode)
Figure3.
Change in arrangement under tensile stress.
Figure 4.
Torque as a superposition of tensile (green) and compressive (red) stress lines.
Figure 5.
Hardware integration
By integrating of all coils into planar PCB-based coil system the repeatability and geometric precision were achieved to make the sensor working without any balancing andproducible in high volumes. The integration of the completesensor electronic into the sensor head makes the system vastly compact and robust against external influences.(Figure6)
The result is an ultra-compact sensor for all mechanical strain situations. They can be used as scales, torque meter, force sensors and further various measurements where mechanical stress is involved.
Figure 6.