Tuesday, March 17, 2020
Hydraulics and Sinusoidal Motion
Hydraulics & Pneumatics: Many test systems use sine wave (sinusoidal) motion. Sinusoidal motion profiles are easy to generate because most computers and PLCs have sin functions either built in or as an additional library. However, generating the motion profile is not the hard part.
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This article is AWESOME, and talks about so many of the things I love about control systems design. Granted, the article can get a bit technical and assumes a bit of a working knowledge of basic control theory, but that doesn't mean we can't get valuable information out of it. First and foremost, the article points out how much stress ANY sinusoidal motion puts on any system. Much of this comes from the exponential effect differentiating trigonometric functions has when high frequencies are involved, hence the frequency-squared term that comes out in the acceleration equation. These are things that apply to any system, hydraulic or otherwise, and shows that we often don't initially see the dynamical issues with a design during a first pass. We often see this when it comes to turntables, because we as humans struggle to scale up angular velocities and accelerations from a model.
The article continues on to discuss other components of a hydraulic system such as valves and their response-frequency. Analogous to audio sampling rates, you want to select a valve that has a frequency response 3-4x the frequency of your system. Additional hydraulic control measures include adaptive sinusoidal control, which is more akin to a phase-shifted response curve. This is useful in that it produces highly accurate results, however at the sacrifice of a delay in response. In our world, this is a calculation that needs to be made. Finally, the author notes that in a hydraulic system we do not need to calculate to the peak flow, but rather only about 70% of the peak.
Clearly I enjoy reading about hydraulics and controls, especially since the two combined create interesting and complex problems to solve.
I wish that I understood this but I really don’t. While reading this, I felt like there was a whole first section of the article that was missing (what is missing is background knowledge, to which I have NONE). I found a few parts interesting and when I stumbled on a section that I relatively understood I mentally thanked my physics teacher in high school for teaching me something that I retained. All I know is that I have very limited knowledge of how hydraulic systems work… What I learned from this article is that hydraulic pumps use frequency and there is a lot of math involved in designing hydraulic pumps. Did this article make me feel dumb? A little. Did I learn something? Yes. Do I understand what I learned? NOT AT ALL. I think I will need to take a physics class to understand what they are saying, or just read more about hydraulic systems. I mean I have the time now that we are all at home
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