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 * Shakers
    * Systems Available for Immediate Shipment
    * Electro-Dynamic Shakers
    * Dual Excitation Shaker Systems
    * Three-Axis Shakers
    * MESA Shaker Systems
    * Power Amplifiers
    * Slip Tables
    * Head Expanders & Fixtures
    * Vibration Control System

 * Chambers
    * Systems Available for Immediate Shipment
    * Temperature/Humidity Chambers
    * Combined Environmental Test Systems
    * Combined System Controller Software
    * Chamber Controller Software
    * EDM Cloud - Remote Monitoring for Chambers

 * Contract Testing & Service
    * Testing & Evaluation Services
    * Electric Battery Testing with CAN bus
    * Installation & Service
    * Demo, Service, & Assembly
    * Testing Lab Photos

 * Resources
    * Reference Materials
    * Common Testing Standards
    * Introduction to Vibration Testing Systems
    * Modal Testing Excitation Consideration
    * What's Required To Bring Vibration Testing In-House?
    * How to Select a Vibration Testing System
    * Sentek Dynamics’ THV Series Environmental Test Systems
    * Selection and Installation of Sentek Dynamics' THV Series Environmental
      Test Systems
    * FEA Animations
    * Installed Systems Gallery
    * Videos

 * About Us
    * News & Activities
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SENTEK DYNAMICS NEWS




MIMO CONTROL NULL TEST ON THREE-AXIS SHAKER SYSTEMS

November 25, 2020 Aakash Umesh Mange - CI Senior Application Engineer

Single axis vibration control tests are widely used to qualify the behavior of
the unit under test (UUT). If the UUT passes the test requirement then it
provides confidence about the sustainability and durability of the test
structure. Excitation in multiple directions is required to test the robustness
of the UUT which has led to the wide use of Multiple-Input Multiple-Output
(MIMO) testing for the programmed test profiles. It is vital to verify that the
hardware setup allows for the unit to be tested in various configurations of
single axis, dual axis, or three-axis. Long hours are required to manually
change the setup because of the involved components (shaker setup, slip table,
driving bar, fixture, etc.) .

Crystal Instruments provides one unique solution. The Control Null feature
provided in Crystal Instruments’ Multiple-Input Multiple-Output Random vibration
control software allows users to perform single axis or dual axis vibration
control tests on a three-axis shaker setup with a simple setup in the software.
The user can perform tests in any direction of interest. With this feature, the
software nulls the selected directions while maintaining the control in the
desired direction(s).

Using the Control Null feature, the target level of the vibration for the
“Control null” channel will be minimized. This allows the user to run the test
with one axis while the other two axis shakers will try to hold and maintain the
shaker to be still on a three-axis shaker configuration. The drives sent to
these control null channels are computed to achieve the lowest possible
responses along the control null direction. The responses in the suppressed
directions will be significantly lower while the dominant direction is still
under control.

Test cases are used to illustrate the efficiency of this feature. A three-axis
electrodynamic shaker system with 20 kN shakers, and a small table-top
three-axis shaker system are used to demonstrate the strength of this
functionality by Crystal Instruments.

Figure 1. Three-Axis Electrodynamic Shaker System

Figure 2. Table-top Three-Axis system

The proficient Spider-80M system by Crystal Instruments’ is a dedicated hardware
for MIMO vibration control testing applications. This chassis features 8 outputs
for maximum efficiency in MIMO testing. The MIMO Random test type from Crystal
Instruments’ EDM MIMO VCS software provides precise, real-time, multi-channel
control for multi-axis random vibration control tests.

Figure 3. Crystal Instruments Spider-80M MIMO Vibration Controller

Test Details
1. A scaled down NAVMAT profile is programmed to run the random vibration
control test. The target level is 1 grms.

Figure 4. NAVMAT Profile

2. First, a single axis vibration control test is run while controlling the
shaker system in the X-direction and measuring responses in other two directions
of Y and Z. This vibration control test is performed on a three-axis
electrodynamic shaker system.

Figure 5. Single Axis (without Control Null) Random Vibration Control test in
X-direction

3. The same profile as shown above is now run while controlling all three
directions on the same hardware setup. The X-axis is controlled to the profile
while the Y and Z directions are set to “control null”.

Figure 6. Three Axis (with Control Null in Y & Z) Random Vibration Control test
in X-direction

4. When comparing the single-axis test and the three-axis test with the Control
null results below, users can observe that the RMS value for the non-dominant
directions (Y and Z) is almost four times lower with the Control Null feature.

Direction Without Control Null (Single Axis Test) - RMS Value With Control Null
(Three Axis Test) - RMS Value Difference X (Control) 9.75 m/s2 9.73 m/s2 N/A Y
2.89 m/s2 0.74 m/s2 Suppressed by 74.4% Z 2.91 m/s2 0.81 m/s2 Suppressed by
72.2%

Table 1. RMS Value comparison for Vibration Control Test with and without
Control Null

For the single axis vibration control test, the “g” value in the non-dominant
directions is 30% of the programmed NATMAT profile. For the three-axis test with
the control null feature enabled, the “g” value in the non-dominant directions
is 8% of the programmed NAVMAT profile. This shows that the Control Null feature
is very efficient in suppressing the response in the non-dominant directions.

5. A similar test as the previous is performed on a table-top three-axis shaker
system. The X and Y directions are “control nulled” while the Z-profile is
controlled to the programmed common carrier profile for the vertical direction.

Figure 7. Three Axis (with Control Null in X & Y) Random Vibration Control test
in Z-direction

The APS and block signals of X, Y and Z directions illustrates that the drives
are tuned in the X and Y directions to suppress the vibration along these
directions, while maintaining the control in the Z-direction.

The results emphasize the efficiency and reliability of the Crystal Instruments’
MIMO Vibration Control Systems. To learn more, please visit
www.crystalinstruments.com/mimo-vibration-control-overview.

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