Operating Deflection Shapes
It is well known that in the case of many types of variable speed machines, there usually are certain speeds at which the machine performs poorly, either evidenced by excessive vibration levels or poor quality of the product. A good example of this is found in the paper industry, where production capacity is reduced because the machine may not safely be operated at certain speeds.
The primary reason for the erratic behavior of complex machines at different speeds is that mechanical resonances in the structure are excited when forcing frequencies approach a natural frequency of the structure. A large machine will have a great many modes of vibration, each one at a particular natural frequency, and it is usually very difficult to determine by inspection how and where the structure is moving at any resonant condition.
Operating Deflection Shape analysis (ODS), is a technique where vibration measurements are made at many locations on a machine, and transfer functions are calculated between a reference location and all the other sensor locations. These TRFs contain phase and amplitude information about the motion of the machine when it is running. The operation of the machine itself provides the excitation forces for the measurement -- unlike FRF measurements, no external excitation is used for ODS.
After the measurements are made, a computer program examines all the data and produces a series of animated 3-D pictures on the screen that shows the motion of the machine parts at selected frequencies. The ODS analysis provides information to the designer about how to modify the structure to solve the vibration problem by pointing out the locations and directions in which the excessive motion is occurring.
Azima DLI provides products and services for Predictive Maintenance including vibration analysis instruments, monitoring and diagnostic software, and consulting for CBM programs.
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