Electrodynamic Vibration Systems
Products
- Air Cooled Series
- Water Cooled Series
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 is 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 ร Acceleration (F = m ร 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 Earthโs gravity is 9.80665 m/sยฒ as per SI and 1 g as per Gravitational Units. Therefore 1 g is equal to 9.80665 m/sยฒ.
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 ๐ฃ = (๐ ร 9806.65) / (2 ร ๐ ร๐)
- For given Frequency and Acceleration, Displacement is derived by ๐ = (๐ ร 9806.65) / (2 ร ๐^2 ร ๐^2)
- For given Frequency and Velocity, Acceleration is derived by ๐ = (2 ร ๐ ร๐ ร ๐ฃ) / 9806.65
- For given Frequency and Velocity, Displacement is derived by ๐ = (๐ฃ) / (๐ ร๐)
- For given Frequency and Displacement, Acceleration is derived by ๐ = (2 ร ๐^2 ร ๐^2 ร๐) / 9806.65
- For given Frequency and Displacement, Velocity is derived by ๐ฃ = ๐ ร๐ ร๐
There are five major components that make an Electrodynamic Vibration System:
Electrodynamic Shaker
An Electrodynamic Shaker converts electrical energy from the Power Amplifier to mechanical vibrations using the principles of electromagnetism as described by Maxwellโs Right Hand Rule and Flemingโs Left Hand Rule. Sdyn has established state of the art infrastructure and realised the technology to design and manufacture any rating of Air or Water Cooled Electrodynamic Shakers. All our Shakers have two separate coils, stationary or Field Coil and dynamic or Armature Coil. When DC current is passed through the Field Coils, it generates a magnetic field as per Maxwellโs Right Hand Rule which magnetises the iron of the Shaker. Sdyn uses two Field Coils with opposing direction of current flow. This architecture adds the flux in shakerโs centre and subtracts it outside the shaker, helping reduce leakage of flux.
The construction of a Shaker ensures that poles created due to magnetism are perpendicular to the direction of current flowing in the Armature Coil. As per Flemingโs Left Hand Rule, the current flowing inside the Armature Coil interacts with the magnetic field lines, causing the armature to move. Changing the direction of the current flowing inside the Armature Coil changes the direction of motion of the Armature.
To realise true sinusoidal motion, the Armature is freely suspended using Rocker based Suspension with nearly negligible axial stiffness and very high cross axial stiffness. Centre is maintained with the help of pneumatics pressure and DC bias to allow for equal movement of the Armature in positive and negative direction.
Shaker body and base are mounted on air bellows and rubber pads which completely isolate all vibrations above 5Hz. For operation below 5Hz, option to lockout the shaker body isolation is provided but Sdyn recommends fixed body shaker mounted on seismic blocks to counter the reaction mass. All Shakers are trunnion mounted to allow operation in horizontal axis and to assist service engineers in maintenance procedures. Rotation can be manual or automatic as per customer preference.
Power Amplifier
Sdynโs Power Amplifiers use compact and extremely efficient Power Modules to multiply the small voltage signal from the Vibration Controller by a fixed gain and deliver it to the Electrodynamic Shaker with the least amount of distortion and noise. Our DSA series Power Amplifier uses solid-state power devices in a Class-D โ Full Bridge configuration. They are Pulse Width Modulated (PWM) at a very high frequency to deliver a wide frequency range starting from DC. Final output is differential and directly compatible with any Electrodynamic Shaker of any make in the world. Modular construction makes these Power Modules easy to handle and active current sharing ensures safe operation when connected in parallel to increase current rating. Integral air cooling ensures continuous duty cycle without sacrificing performance at peak temperature and humidity.
These Power Amplifiers are compatible with any make of Electrodynamic Shakers due to their extremely low output impedance and are fully configurable by the password protected Manufacturerโs Interface at customer site. This interface allows the user to change the state and status of any protection, making our Power Amplifier the ideal choice for Replacement Power Amplifiers.
Assembled in industry standard 19โ racks, all modules of our Power Amplifier are rack mountable. Removing and installing modules is made easy via guide rails on which every module is designed to slide. Designed to meet international design and safety standards, every section of our Power Amplifier is feature rich and contains a host of protections for operational safety, flexible integration, and easy serviceability.
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.