How to derive the first natural frequency requirement of a subassembly?

Question

How to derive the first natural frequency requirement of a subassembly?

Ionut Cosmin (Aerospace)

(OP)

8 Nov 22 18:04

Hello all,

I am trying to determine what should be the first eigen mode frequency for a subassembly if the requirement is known for the assembly.

For example, let' say I have a robotic arm which has a requirement that the first natural freq should be higher than 70 Hz. On this arm I have an equipment, let's say a camera. How do I determine the requirement for minimum freq of the camera? is there an equation that can provide this answer? or should I just take the same requirement from the main assembly, the arm?

Thanks,
Cosmin

GregLocock (Automotive) · Answer 1 · 2022-11-08 20:53:06

While it would be expected that the camera's modes would be >70 Hz, the main effect is its mass on the bending mode of the arm. 70 Hz seems incredibly high, perhaps that is driven by the camera.

Cheers

Greg Locock

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SWComposites (Aerospace) · Answer 2 · 2022-11-08 22:02:48

both the camera and the assembly have to have first natural freq > 70 Hz. if the first mode of the camera is ~ 70 Hz, you will likely have difficulty with the assembly frequency.

IRstuff (Aerospace) · Answer 3 · 2022-11-08 22:20:42

The alternative is to put the assembly or the camera on isolators and/or stabilization system; the US Army used to have an EO sensor mounted on the rotor shaft and it had 8-Hz isolators, and coupled with its active stabilization servos could maintain nearly undetectable vibration levels, at least, good enough to kill Iraqi tanks from a looong distance

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How to derive the first natural frequency requirement of a subassembly?