An effective auto-tuning process ensures high performance and stability even as specimen stiffness changes throughout the range of compression.
MTS Acumen™ Test System:
In this Q&A, MTS Product Engineer Andrew Simon discusses a recent MTS Acumen product demonstration that changed a biomedical customer’s experience with electrodynamic actuation.
An Exceptional Experience with Electrodynamic Actuation
Q: Based on your recent experience demonstrating MTS Acumen test systems, what is the appeal of electrodynamic actuation in test labs and what are some of the challenges?
Simon: Electrodynamic technology, which provides the user with higher performance capability than servohydraulic technology, can be quickly and easily integrated into test labs because it can be installed and used in any location with a conventional electrical outlet, consumes less energy than other technologies, and systems require minimal maintenance.
Often these benefits are over-shadowed as many test engineers associate electrodynamic systems with lack of overall control, poor response to limits, and ineffective auto-tuning processes. Recently we were approached by a biomedical materials manufacturer in Europe that had been experiencing these issues to such a degree that it discontinued the use of its electrodynamic system. During our visit we demonstrated the performance levels of the MTS Acumen Test System and how it resolved these common user issues, renewing the lab’s interest in electrodynamic actuation.
Q: Why is overall control considered a challenge with electrodynamic actuation and how does MTS Acumen technology address this challenge?
Simon: Specimen stiffness can change over the course of dynamic tests which presents a performance challenge for most systems. For stability, specimens must be tuned in the high-stiffness region but that tuning traditionally results in low performance when the specimen reaches the low-stiffness region during the test.
This problem was one of the customer’s primary concerns. We demonstrated MTS Acumen system’s ability to perform by testing a tennis ball because its stiffness changes throughout the range of compression.
We opened the user-friendly MTS TestSuite™ software application and tuned the tennis ball in the high-stiffness region, and executed the test through to the “softer” regions. The MTS Acumen system demonstrated great performance and stability through the entire stiffness range. The advanced tuning and control techniques provide stability and high performance across a wide operating window, resulting in more accurate test data.
Q: How does the test system response to limits affect the user-experience? Why does this occur with most electrodynamic systems, and how is it resolved by the MTS Acumen system?
Simon: Electrodynamic actuation is capable of extremely high-performance and high speed, but with that performance and speed comes the possibility of unintentionally breaking specimens or fixtures. In biomedical testing, the complex specimen structure and geometry makes traditional limits inadequate for specimen protection. These issues often resulted in broken specimens. Where the specimen and test conditions make specimen protection a challenge, the MTS Acumen system excels.
To demonstrate the MTS Acumen system’s superior response to limits and failure detection, we forced the system into an unstable state to prompt a controlled stop, which leverages an advanced interlock method developed by MTS. The instant the instability was detected, the system locked in its current position and remained under control, with no freewheeling and essentially no additional load applied to the specimen. Both the equipment and the specimen were safe from harm because the machine remained in control at all times.
Q: Describe the auto-tuning shortcomings often associated with electrodynamic systems. How does the MTS Acumen system compare?
Simon: The customer commented that their experience with auto-tuning on other electrodynamic systems seemed inflexible and not as sophisticated. As a result, they were unable to reliably tune and test anything but specimens with very limited variation.
In contrast, the MTS TestSuite software used with the MTS Acumen system is designed to measure multiple specimen and system characteristics for auto-tuning purposes, resulting in more appropriate tuning values. We opened the MTS TestSuite interface and showed the customer how the auto-tuning process incorporates specimen-specific measurements as part of the setup process, facilitating greater accuracy and customization for a specific test. With MTS auto-tuning, the software displays the accuracy of the tuning with an intuitive blue, green and red scale. Adjustments can be made with drag and drop simplicity. For the most complex specimens, the MTS Acumen system is unique in allowing the user full tuning and adjustment control, which results in the ability to tune specimens that previously could not be run on electrodynamic systems.
Q. What about the issues with overheating that can be common with electrodynamic actuation?
Simon: MTS designed the cooling system to support the full force ratings. That means that the MTS Acumen system will run indefinitely at its maximum rated force and frequency without overheating. Many other electrodynamic systems have a maximum load that can only be achieved for short periods of time without overheating.
Q. Why has MTS been so successful at addressing these issues?
Simon: I believe the exceptional performance of the MTS Acumen system is the result of our advanced product development process focused on a superior quality product and include a rigorous testing and validation phase. During development, we carefully assessed what users were experiencing in the field with comparable systems, and our engineers dedicated the time and resources necessary to address each issue, always keeping integrated system performance as a goal.
The MTS Acumen system is also a product of MTS’ unmatched controls and technology leadership in servohydraulic and electromechanical actuation. We applied this extensive experience to successfully develop advanced control techniques which are fully integrated hardware and software solution. These control techniques take this electrodynamic system design to the next level of performance and usability.
Q. What is the takeaway for other material test labs?
Simon: This is exciting news for material test labs. They can now leverage all the advantages of electrodynamic actuation, without the shortcomings that may have caused them to delay acquiring this technology in the past. With the MTS Acumen system, all issues with control, response to limits, auto-tuning and overheating have been effectively addressed and overcome.
What’s more, this technology is not only different, but also better. Many of our customers have reported discovering new specimen behaviors due to the high performance of MTS Acumen systems.
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