Comparison of Measurement Methods for Evaluating Displacement of Commercial Vehicle Seats

Measuring the displacements in vehicle seat suspensions and the displacements the seat has to absorb may assist vehicle seat designers in better designing seats to absorb vibrations. Low frequency seat displacement is important in seat design to identify end-stop events and higher frequency shorter displacements are also important since seat components can be optimized to absorb these smaller displacements. Displacements can be directly measured with special instruments, but it would be less complicated if simple, compact accelerometers could be used to measure the seat displacements. This paper compares accelerometer-derived displacement measurements to known displacements derived from sinusoidal physics and field measured random displacements measured with potentiometers. Using known, controlled sinusoidal displacements, three lab-based experiments were conducted to determine how well accelerometers, using double integration, could measure displacements. In addition, using a vehicle travelling on four different road types, the capability of accelerometers measuring random displacement was assessed. In general, the accelerometer-derived displacements matched the known sinusoidal displacement in the lab settings and the potentiometer measured displacements in the field; however, limitations were identified. First, the frequency bandwidth of the accelerometers can be a limitation. Most accelerometers are limited in their ability to measure low frequency vibrations (0 - 3 Hz) so MEMS-based accelerometers with DC resolution may facilitate better capture of the low frequency displacements. Second, the direct displacement measurements need to be more robust. Potentiometers can be prone to errors due needed signal filtering and additional errors if not correctly mounted and calibrated. With the uncertainty associated with displacement measurement, more systematic evaluation is needed to determine the viability of various transducers for measuring absolute and relative vehicle seat displacements.