Steve Trout, Sr. Application Engineer,
MTS Systems Corporation
MTS Acumen Test System with MTS EnviroBath
Fine Wire Test on MTS Acumen Test System
Advantages of Electric Actuation in Low-Force Testing ApplicationsMTS Senior Application Engineer Steve Trout has more than 35 years of experience responding to the needs of materials researchers and biomedical device manufacturers. In this Q&A, Trout discusses the unique advantages electric actuation brings to low-force testing applications.
Q: Is electric actuation a new technology?
A: Although it is not new technology, it has been used in testing applications for less than a decade. It has taken some time for electrically actuated test systems to handle the precise force and motion requirements of materials testing. These systems are a particularly good fit for biomedical testing. They are specifically designed for lower-force, high-frequency testing with high fidelity, which is exactly what many customers in this industry need.
Q: What improvements have made electric actuation more accurate?
A: The primary challenge with electric actuation is control. Moving an actuator up and down with electricity instead of servohydraulics is not difficult. But it is very hard to provide actuation with enough accuracy for material testing. Precise control is a function of the controller and the software. The better these components are, the better you will be able to control the parameters of the test system, the better the system will behave and the better the data will be.
Q: What advantages does electric actuation offer compared to servohydraulic?
A: One of the most important is the lack of oil. There is no oil to dispose of or recycle. In biomedical testing, an oil leak could contaminate the specimen, or the saline solution bath, or the bovine solution. Now you can avoid those issues entirely. Electric actuation is also very quiet and clean. With MTS Acumen™ Test Systems, there are no hoses or hardline and the cables are all embedded within the load frame. These more aesthetic aspects are important because the test lab is often a showpiece for visiting surgeons, who tend to appreciate an uncluttered environment.
Q: Are there other ways Acumen test systems improve control?
A: Yes, these systems can easily handle frequencies from 50 to 100 Hz. The controller is the same controller we use with our servohydraulic test systems, so it will be familiar to those who already use MTS test systems. Another important difference is the fact that customers can run up to four Acumen load frames independently with a single controller. This ability to provide all that control within a single console provides a space advantage for smaller labs. It also adds scalability for labs that want to increase test capacity without buying an additional controller each time they add a load frame.
Q: How does autotuning affect the process?
A: Autotuning is another way to improve the accuracy of test results. Materials and biomedical tests need to hit peaks and valleys consistently in order to generate reliable data. The autotuning feature on Acumen test systems includes three parameters — mass, stiffness and damping — to help ensure the best possible control and most accurate specimen response. This patented autotuning method examines the entire load train for all three parameters. Of course, customers can always tune the system manually if they prefer.
Q: Can you give an example of how these feature work in a real application?
A: Precise control comes to life when the specimen in question has variable stiffness. Think about a prosthetic implant with an interior rubber bladder protected by a hard stop bumper. When it is first compressed, the specimen is soft and compliant. Then when you hit the bumper, it becomes very stiff. The stiffness changes considerably throughout the test, which makes it difficult to evaluate whether the bladder has been manufactured correctly. Accurate control helps customers develop a test profile that replicates the actual performance, so they can produce more realistic test data.
Applications for Acumen
MTS customers are already using the Acumen test system to perform mechanical tests in a wide range of low-force applications, including all of the following:
• Orthopedic constructs and related materials
• External fixation devices
• Staples for small joints
• Dental implants
• Implantable devices: lead testing and life testing up to 600 million cycles
• Shape memory alloys
• Fine wire testing
• Biomechanical testing for small bones and tissues
• Elastomeric components for prosthetics
• Testing on human cadavers: bones, skin, tissue
• Fatigue and tensile materials testing for polymers and metals
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