Electrodynamic shakers can be in different shapes, such as standard shakers, modal shakers or inertial shakers. Depending on the area of use, one of these shaker types must be selected for the test.
Tests with standard shaker can be driven at different frequencies and amplitudes. In these tests the test specimen can be directly fixed to the shaker armature and vibrating surface area can be enlarged by using a head expander according to the specimen sizes. The vertical excitation can be translated into horizontal excitation by using slip table. In some cases, instead of changing the direction of the motion of the vibration, the part may be rotated and tested. The duration of the test and vibration levels are determined from test standards or real time measurements.
Modal shakers are used in the study of vibration behavior of structures. No test specimen is mounted on such shakers. These shakers are mounted to the structure with a stinger and force is transferred from the shaker to the structure via this stinger. The structure under test and / or the modal shaker can be hung with components such as an elastic rope or spring during the test to simulate free-free boundary conditions. In this way it is possible to excite the test sample at different frequencies. As a result, the natural frequencies and mode shapes of the structure can be calculated with the vibration values measured over the structure.
Inertial shakers and modal shakers are similar in usage area. They are used also in tests for examining vibrational behavior of structures such as modal shakers. However, compared to the modal shakers, the connection styles are different. The inertial shaker’s own body vibrates. For this reason, inertial shakers are fixed directly to the structure. It is easier to use than modal shakers. Depending on the dimensions of the structure and the desired excitation frequencies and levels, modal shakers or inertial shakers can be used for vibration testing.