The main errors of MEMS accelerometers are misalignments of their sensitivity axes, thermal and long-term drifts, imprecise factory calibration, and aging phenomena. In order to reduce these errors, a two-axial tilt sensor comprising a triaxial MEMS accelerometer, an aligning unit, and solid cubic housing was built. By means of the aligning unit it was possible to align the orientation of the accelerometer sensitive axes with respect to the housing with an accuracy of 0.03°. Owing to the housing, the sensor could be easily and quickly recalibrated, and thus errors such as thermal and long-term drifts as well as effects of aging were eliminated. Moreover, errors due to local and temporal variations of the gravitational acceleration can be compensated for. Procedures for calibrating and aligning the accelerometer are described. Values of thermal and long-term drifts of the tested sensor, resulting in tilt errors of even 0.4°, are presented. Application of the sensor for monitoring elevated loads is discussed.
Values of static and kinetic friction coefficient in micro slide bearings, consisting of journals and bushings (with the diameter of 3.5 mm) made of pairs of 5 polymer materials (16 chosen combinations of PA11, ABS, PC, PS and PETP), were determined. A method of measuring static and kinetic friction coefficient, at various values of: load, rotational speed, and standstill time, as well as the structure of a dedicated test rig, were discussed. Chosen mechanical properties of polymers measured using indentation method, and conclusions from the conducted experiments, are shown. The presented results provide key information for a proper choice of polymer materials, which are to work as a friction node. The biggest observed difference in the moment of friction among the tested slide bearings reached almost 40% (with respect to the highest value).
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