- #1
Juanda
Gold Member
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- TL;DR Summary
- There are commercial shakers that claim to be able to accomplish 6-DoF, but I don't understand the underlying mechanism that makes it possible.
In vibration tests, most of my experience is working with uniaxial machines. You get results in the other directions by reorienting the test element, the machine, or both. This can be annoying at least and risky at most.
For in-plane motion, you run the test twice with a sliding table turning the test element 90 degrees, and for the out-of-plane test, you turn the shaker and install a head expander instead of a sliding table.
The following picture shows a configuration like the one I described. You can see the sliding table and the shaker oriented upwards with a head expander installed.
There are some shakers out there that are supposed to be able to accomplish 6 degrees of freedom (DoF), but I don't understand how it's possible. I'm referring to instances like this one.
I don't understand what's going on inside that kind of shaft boot. For the table to move in all directions, the simplest thing would be to have a flexible element joining it to the shaker, but that could go bad in many ways since it'd interact with the vibration input. So it has to be something rigid but compliant with the 6-DoF. I have been trying to understand what kind of joint would allow that, but I haven't had any luck yet. They mention spherical bearings, so maybe it's just an articulated joint under the boot, but I don't feel like that would be enough.
On the other hand, there are systems like this one, which I think I can imagine what's going on under the tarp. I have the feeling it must be a Stewart platform. I have no way to verify it, but it's how I'd try to do it, and I'd say the dimensions under the tarp check out.
Thanks in advance
For in-plane motion, you run the test twice with a sliding table turning the test element 90 degrees, and for the out-of-plane test, you turn the shaker and install a head expander instead of a sliding table.
The following picture shows a configuration like the one I described. You can see the sliding table and the shaker oriented upwards with a head expander installed.
There are some shakers out there that are supposed to be able to accomplish 6 degrees of freedom (DoF), but I don't understand how it's possible. I'm referring to instances like this one.
I don't understand what's going on inside that kind of shaft boot. For the table to move in all directions, the simplest thing would be to have a flexible element joining it to the shaker, but that could go bad in many ways since it'd interact with the vibration input. So it has to be something rigid but compliant with the 6-DoF. I have been trying to understand what kind of joint would allow that, but I haven't had any luck yet. They mention spherical bearings, so maybe it's just an articulated joint under the boot, but I don't feel like that would be enough.
On the other hand, there are systems like this one, which I think I can imagine what's going on under the tarp. I have the feeling it must be a Stewart platform. I have no way to verify it, but it's how I'd try to do it, and I'd say the dimensions under the tarp check out.
- Do you understand the joint used in the first 6-DoF machine?
- Which of the two methods do you think is preferable to get 6-DoF for testing? The traditional shaker definitely looks stronger and more solid, but the Stewart platform seems like a straightforward application of 6-DoF movement.
- Do you think there is a better alternative to the two options shown here?
Thanks in advance
