Construction of a portable test rig to perform experimental modal analysison mobile agricultural machinery

Higher working speeds of mobile off-road vehicles arouse dynamical problems like excessive vibrations, which decrease the vehicle lifetime, the driver 's comfort, and the working precision. Testing the vibration behaviour of p resent vehicles is an indispensable source of knowledge for further improve ment of vehicle dynamics. More restrictive legislation concerning allowable exposure of drivers to vibrations raises the need for these tests. For sma ll- and medium-sized companies the required know-how and equipment is too e xpensive and vibration analysis of their products has to be farmed out. Sin ce tests in situ have many advantages, a prototype of a mobile low power te st rig for experimental modal analysis on vehicles is described in this pap er. The vehicle under test is excited vertically under one of its wheels wh ile the other wheels rest on stationary platforms. The power saving by usin g an airspring parallel to the actuator is investigated by including a mode l of the airspring in the equations of motion of the test rig. It turned ou t that the power saving due to the airspring is proportional to the relatio n of the acceleration due to gravity to the maximum acceleration of the exc itation signal. For small band excitation signals extra power savings can b e achieved by connection of the airspring with a pressure vessel which opti mal size depends on the frequency content of the excitation signal. Experim ents with a prototype of the vertical shaker demonstrate that the different modeshapes of a tractor-sprayer combination can be sufficiently excited an d modal analysis was performed successfully. (C) 1999 Academic Press.