Posts
Identification of a Flexible Robot Arm Dynamics
Background
Accurate modeling of flexible robot arms is essential for high-precision motion control and vibration suppression in industrial automation and robotic applications. Our Frequency Domain Identification Toolbox provides sophisticated tools for extracting reliable dynamic models from experimental frequency response data.
The Challenge
In this case study, we needed to identify the dynamic behavior of a flexible robot arm by:
- Characterizing the relationship between applied torque and resulting acceleration
- Capturing multiple resonance modes accurately
- Determining optimal model order for control system design
- Accounting for actuator limitations at resonance frequencies
Measurement Setup
The experimental setup consisted of a controlled torque input applied to the vertical axis at one end of the arm, with tangential acceleration measured at the other end.
A multisine excitation signal was used with frequency components from 0.122 Hz to 24.3 Hz. Ten periods of data were collected to ensure sufficient information for robust identification.
Solution Approach
Using our Frequency Domain Identification Toolbox, we systematically explored different model structures:
1) Initial Model Assessment: Analysis of the nonparametric frequency response indicated at least two complex pole pairs and two complex zero pairs would be necessary, suggesting a starting model order of 4/4.
2) Model Refinement: While the initial model provided a good fit, we observed mismatches at higher frequencies, leading us to incrementally increase model orders.
3) Automated Order Selection: We leveraged the toolbox’s automated model comparison capabilities to evaluate multiple candidate models simultaneously, eliminating significantly underperforming models.
4) Uncertainty Analysis: The toolbox’s ability to visualize confidence regions for poles and zeros helped identify parameters with higher uncertainty, guiding the final model selection.
Results
The toolbox successfully identified several viable models with different tradeoffs:
-
- Model 6/6 showed slightly better performance based on the MDL criterion
- Confidence region visualization revealed a pole pair with larger uncertainty
- Multiple models provided comparable frequency response fits
Conclusion
This case study demonstrates how our Frequency Domain Identification Toolbox enables engineers to identify complex flexible structures with multiple resonance modes. The comprehensive comparison tools help users make informed decisions about model order selection based on quantitative criteria and uncertainty analysis, resulting in reliable models suitable for advanced control system design.