Vibration Tips
Electrodynamic Vibration System
An Electrodynamic Vibration System generates controlled vibrations to simulate real life conditions in a laboratory environment. For any object meant to operate dynamically in its environment, vibration testing is a useful tool. These systems allow us to precisely re-create, accelerate, and manipulate the vibration an object will experience in its entire lifespan, inside a laboratory. This helps in identifying and isolating weakness of an object in areas such as mechanical design, metallurgy, mounting, heat or chemical treatment, welding, bolting, assembling, etc.
An Electrodynamic Vibration System and an Audio System are similar in their basic principle. In an Electrodynamic Vibration System, the Electrodynamic Shaker works like the speaker of an Audio System. A Vibration Controller generates the signal that is fed to a Power Amplifier of an Electrodynamic Vibration System like an iPod or any Music Player giving its audio signal to the Power Amplifier of an Audio System. The Power Amplifier drives the Armature Coil of an Electrodynamic Shaker in an Electrodynamic Vibration System and the Voice Coil of a Speaker in an Audio System.
The main purpose of an Electrodynamic Vibration System is to create vibrations and the main purpose of an Audio System is to create sound. One major difference between the two is that, in an Electrodynamic Vibration System, a sensor is placed on the Armature of the Electrodynamic Shaker to sense the generated vibrations and provide feedback to the Vibration Controller to keep everything in a closed loop control, whereas, an Audio System operates in open loop.
Mechanism of an Electrodynamic Vibration System
The basic formula behind calculating required force rating of an Electrodynamic Vibration System is Force = Mass × Acceleration (F = m × a).
- The unit of Force (F) is Newton (N) as per SI and kgf as per Gravitational Units.
- The unit of Acceleration (a) is m/s2 as per SI and g as per Gravitational Units.
- The unit of Mass (m) is kg for both SI and Gravitational Units.
The Earth’s gravity is 9.80665 m/s² as per SI and 1 g as per Gravitational Units. Therefore 1 g is equal to 9.80665 m/s².
In order to determine required system rating for a customer, the same formula is applicable. Every customer will have an object, its fixture, and the test profile they want to run. With this information in hand, the process of determining a system is:
- Step 1. Determine the size of Head Expander and Horizontal Slip Table needed based on the dimensions of the fixture and object.
- Step 2. Determine the smallest Electrodynamic Vibration System which is compatible with the chosen Head Expander and Horizontal Slip Table.
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Step 3. Add all the masses for vertical and horizontal orientation separately:
a. Vertical: armature + head expander + fixture + object
b. Horizontal: armature + HST coupling + HST bed + HST bearings + fixture + object - Step 4. Multiply total mass for vertical and horizontal orientation with the maximum acceleration level of the test profile.
- Step 5. If the resultant force rating, for either of the orientation, is within 80% of the force rating of selected system, please proceed with the selected system.
- Step 6. If the resultant force rating, for either of the orientations, is above 80% of the force rating of the selected system, please choose a higher rating system and redo the calculation from Step 3.
In the above shown working, we have only considered the acceleration component of a profile. At low frequency, it is necessary to ensure that the resultant displacement and velocity due to acceleration is within the system capability. The following formulas help convert these values between each other:
- For given Frequency and Acceleration, Velocity is derived by 𝑣 = (𝑔 × 9806.65) / (2 × 𝜋 ×𝑓)
- For given Frequency and Acceleration, Displacement is derived by 𝑑 = (𝑔 × 9806.65) / (2 × 𝜋^2 × 𝑓^2)
- For given Frequency and Velocity, Acceleration is derived by 𝑔 = (2 × 𝜋 ×𝑓 × 𝑣) / 9806.65
- For given Frequency and Velocity, Displacement is derived by 𝑑 = (𝑣) / (𝜋 ×𝑓)
- For given Frequency and Displacement, Acceleration is derived by 𝑔 = (2 × 𝜋^2 × 𝑓^2 ×𝑑) / 9806.65
- For given Frequency and Displacement, Velocity is derived by 𝑣 = 𝜋 ×𝑓 ×𝑑
There are five major components that make an Electrodynamic Vibration System. These are mentioned below:
Electrodynamic Shaker
An Electrodynamic Shaker converts electrical energy from the Power Amplifier to mechanical vibrations using the principles of electromagnetism as described by Maxwell’s Right Hand Rule and Fleming’s Left Hand Rule.
Power Amplifier
A Power Amplifier is a Class-D – Full Bridge – Switching Amplifier which multiplies the voltage output of the Vibration Controller by a fixed gain, with great efficiency and high current capability, as required by the Electrodynamic Shaker.
Head Expander
A Head Expander is bolted to the Armature head for increasing the platform size in the vertical orientation for testing in Z axis. A Head Expander can be Non-Guided or Guided of Square or Circular shape.
Horizontal Slip Table
A Horizontal Slip Table is a frictionless platform used for vibration testing in X and Y axis. The Electrodynamic Shaker turns from its vertical orientation to a horizontal orientation to couple with a Horizontal Slip Table.
Vibration Controller
A Vibration Controller allows the user to create a test profile on a PC and generates a signal in real time to match the test profile. An Accelerometer on the Electrodynamic Shaker provides feedback to keep the system under closed-loop control.