Vibration shakers play a crucial role in various industries and their operation is rooted in the fascinating world of engineering. They are indispensable for applications like vibration, shock and environmental testing and dynamic characterization of mechanical structures.
Vibration testing can be performed for 3 main purposes. Firstly, during modal testing engineers investigate the natural frequencies and mode shapes of the device. Secondly, vibration testing assesses the device under operational conditions. Lastly, it helps determine the device’s endurance under prolonged vibration, conducting endurance tests to evaluate its fatigue life.
What is an electrodynamic shaker?
Electrodynamic shakers are instrumental in simulating the real-world environmental conditions that products and structures might encounter during their operational life. But how do they create those precise vibrations that are so essential for testing and research?
At the core of an electrodynamic shaker is a component called a voice coil. Much like the voice coil in a speaker, this critical element converts electrical currents into physical vibrations. The concept behind this conversion is the use of electromagnets.
Understanding Voice Coils
The main strengths of voice coil is extreme accuracy and high movement speed. Voice coils move by using Lorentz force which is created by placing a coil of wire in a fixed magnetic field. When current is put through the coil it turns into a electromagnet making it either be repelled or attracted to the fixed magnetic field giving you a force.
Understanding Electromagnets
The voice coil component of a speaker is actually just an electromagnet. Electromagnets are coils of wire, and they’re normally wrapped around some kind of magnetic metal, like iron. By running an electrical current through the wire, you produce a magnetic field surrounding the coil; this field magnetizes the metal in the middle creating north and south polar orientations. The difference between an electromagnet and a permanent magnet is that you can switch the polar orientations on an electromagnet by reversing the current’s flow.
Design Considerations
The design of an electrodynamic shaker is a careful engineering process with several key considerations; a combination of cooling methods, magnet types, frequency bandwidth, dynamic performance, control systems, signal processing and structural integrity.
- Force Level: The required force level determines the shaker’s cooling method. If the force level is below 70kN, air cooling is sufficient. Beyond this threshold, water cooling is necessary for maintaining optimal performance.
- Permanent Magnets: For force levels below 500N, permanent magnets can be used. These magnets provide a stationary magnetic field, simplifying the design. However, for higher force levels, a field coil is required to create the necessary magnetic field.
- Frequency Bandwidth: This refers to the range of frequencies or vibrations that a shaker can produce. A broader frequency bandwidth means the shaker can generate vibrations over a wider range of frequencies.
- Dynamic Performance (Acceleration and Displacement): The dynamic performance of a shaker includes considerations of acceleration and displacement. Higher force levels often correlate with higher acceleration capabilities and larger displacement amplitudes, enabling the shaker to simulate a wider range of real-world conditions.
Design Considerations
Electrodynamic Shaker Design Process:
1- Required force, F=ma (Air cooled/Water cooled-Magnet/Coil)
2- Required frequency bandwidth (Suspension/Guidance design)
3- Unbalance mass (Suspension and bearing design)
Electrodynamic shaker design starts with the required force level. If the force level is below 70kN, the shaker can be air cooled otherwise water cooling is required. Furthermore, the force level decides whether a permanent magnet can be used or not. If the force level is below 500N a permanent magnet is available otherwise the stationary magnetic field has to be created by a field coil.
The frequency bandwith is dependent on the guidance system and the suspension design. Without a guidance system the shaker will have a low frequency bandwith.
Lastly, if the shaker will support an unbalance mass it will further need some bearings to support the unbalance moments.
Why Vibration Shakers Matter
- Product Testing and Validation: Vibration shakers are instrumental in subjecting products, components, and structures to controlled vibrations and shocks. This testing process helps engineers and manufacturers identify weaknesses, ensure product durability, and enhance overall quality.
- Environmental Simulation: They are invaluable for simulating the environmental dynamics that products might encounter during their operational life. From aerospace to automotive industries, these simulations are vital for developing and validating products designed to withstand harsh conditions.
- Dynamic Characterization: Vibration shakers enable precise dynamic characterization of mechanical structures. Researchers can assess the behavior of materials and structures under various load conditions, leading to improved designs and safer structures.
