Tips for Selection

 

In reality, many machines, machine components, machine accessories, etc. are exposed to vibrations or generate vibrations themselves. The longer lifespan of structures, comfort parameters related to their use depend on their response to vibrations, their vibration resistance. Concepts such as looseness, resonance, mechanical tuning, transfer function, aging (detuning, deformation), fatigue fracture arise in connection with this.

 

By using shakers, the object under examination can be excited in a precisely known direction, with a defined signal shape, amplitude, and frequency. All this can be done in laboratory conditions, controllably (with many measurement and recording options), reproducibly, and in a way that can be separated from other environmental influences.

 

The structure of electrodynamic shakers shows many similarities to an everyday loudspeaker, but visibly more robust. The heart of the shaker is a fixed stator coil, in which the moving armature coil is located. The current flowing through the stator coil induces voltage in the armature coil. Due to its own short circuit, current also flows in the armature coil due to the induced voltage, thus creating opposite polarity electromagnetic fields around both coils. This generates the force required for the displacement of the armature coil in the direction of the coil's central axis.

 

Low-force electrodynamic shakers are mainly found in educational or research institutions, as well as in calibration laboratories. Medium-force electrodynamic shakers can be used for vibration testing of medium-weight objects, with sufficient fan ventilation for cooling, hence these types are also referred to as air-cooled electrodynamic shakers. For high-power electrodynamic shakers, coil cooling must be achieved with water cooling, as the high accelerations and/or large masses to be moved lead to such energy density that the heat losses cannot be dissipated by air cooling.

 

Operating large shakers requires a large amount of energy, so (through the power amplifier that defines the theme of this chapter) they are able to draw high electrical power from the grid and convert it into heat during operation. Therefore, it is worth choosing the parameters of the shaker well for the given task.

 

To create movements corresponding to the desired signal shape, based on the measurement of the shaker-armature movements, the control unit modifies the control signal until the measured movement of the shaker matches the desired signal shape. This control process is also called closed-loop feedback control. Absolute or relative vibration sensors or displacement sensors can be used to measure the movements and deformations of the shaker and the object under test. Modern shaker controllers support a wide variety of sensor types for this purpose:

- absolute vibration sensors, - relative vibration sensors / distance sensors, - other sensors.