Operational Deflection Analysis (ODA) is a technique used to determine and visualize the dynamic behaviour of structures during operation by means of vibration measurement on a representative number of positions on the structure with subsequent processing of the data to yield relative magnitudes and phase relationships, which, in turn, facilitates reliable and calibrated visualising of the actual structural response.
Unlike traditional modal analysis, which mostly relies on impulse excitation using a modal hammer, ODA implements in-situ vibration and operational forces acting on the structure. This article explores the ODA techniques applied in a recent structural dynamic analysis of a 3D concrete printer, highlighting how these methods can improve machine performance and stability.
The primary challenge addressed in this case study was the root cause analysis of large nozzle vibrations in the 3D concrete printer which led to poor quality prints.
Operational Deflection Analysis as applied to a large 3D printer structure
Data Acquisition:
This involves the measurement of structural response using accelerometers. In the case of the 3D concrete printer, the setup included 10 tri-axial MEMS accelerometers positioned on carefully selected locations (representative of the entire structural and mechanical system) to capture the vibrational response throughout the printer structure, including the printer head, gantries, and support columns.
Data were recorded during specific transient and steady operating manoeuvres to ensure a comprehensive dynamic characterisation.
Signal Processing:
The raw data from the sensors are processed to calculate acceleration values, integrated displacement time traces, and frequency domain transfer functions.
Transfer functions between different measurement points establishes the relative magnitude and phase relationship between the different points on the structure, which, in turn facilitate the calculation of the deformation modes of the structural components making up the system.
The analysis identified several dominant response frequencies with corresponding operational deflection shapes. It should be noted that the total structural response is made up of a range of operational deflection shapes (at different frequencies) which all needs to be characterised and “ranked” in terms of relevance.
Interpretation:
The obtained results highlighted the contributions of different structural elements and associated deformation modes to the overall dynamic response, such as the deflection of vertical columns and the interactions between the printer head and the gantries.
The ODA results were compared with the results obtained from a transient dynamic finite element analysis of the system and serves to calibrate and validate the FEM, which in turn, enabled the OEM to introduce intelligent and effective design upgrades.
Benefits of Operational Deflection Analysis
Operational Deflection Analysis is an exceedingly useful technique and are very well suited for industrial application and diagnostics:
Realistic Conditions: ODA captures the dynamic behaviour of structures under actual operating conditions, offering accurate and realistic insights into the structure’s behaviour and response.
Non-Intrusive Testing: Since ODA relies on existing operational forces, it avoids the need for artificial excitation, making the testing process less invasive and more practical for large structures.
Comprehensive Analysis: By capturing a wide range of operational scenarios, ODA provides a thorough understanding of the structure’s vibration characteristics, facilitating targeted improvements.
Identification of Weak Points: The analysis can pinpoint specific areas of the structure that contribute to undesirable vibrations, enabling targeted reinforcements or design modifications.
Optimising Operations: Understanding the dynamic behaviour allows for adjustments in operational parameters to minimise vibrations and enhance overall stability.
Conclusion
Operational Deflection Analysis is a powerful tool for diagnosing the structural behaviour and performance of industrial machinery.
It provides a realistic and comprehensive understanding of dynamic behaviour and facilitates targeted improvements and informed design decisions.
The application of ODA techniques in the analysis of the concrete 3D printer demonstrated its potential to significantly enhance machine stability and operational efficiency.